feat(cache): add shared S3-compatible storage (#1244)

Store the cache used by `actions/cache` in an S3-compatible bucket such as AWS S3 or RustFS, with no `cache-server`. Runners with the same settings use the same cache.

A cache saved on one runner can be restored on the others within 30 seconds. The runner talks to the bucket over the S3 REST API with SigV4, without an SDK. Lifecycle rules on the bucket expire old caches.

*Description rewritten by Claude.*

---------

Co-authored-by: silverwind <me@silverwind.io>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1244
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>
Co-authored-by: bircni <bircni@icloud.com>

README.md

@@ -341,6 +341,24 @@ cache:
 
 Runners can also share one `cache.dir` on a file system with working file locks, at the cost of slower cache requests.
 
+**Storing the cache in an S3-compatible bucket**
+
+The cache can also be stored in an S3-compatible bucket such as AWS S3, MinIO or RustFS, with no cache server. Runners with the same settings use the same cache:
+
+```yaml
+cache:
+  s3:
+    endpoint: "http://minio:9000"
+    region: "us-east-1"
+    bucket: "runner-cache"
+    prefix: "gitea-runner-cache"
+    path_style: true
+    access_key_file: "/run/secrets/cache-s3-access-key"
+    secret_key_file: "/run/secrets/cache-s3-secret-key"
+```
+
+A cache saved on one runner can be restored on the others within 30 seconds. The eviction settings below do not apply to the bucket, so add lifecycle rules to it that expire old caches and abort incomplete multipart uploads.
+
 **Eviction**
 
 Entries not read or written within `retention` (default `168h`) are removed. A repository over `repo_size_limit` (default `10GB`) loses its least recently used entries, and `size_limit` (off by default) caps the whole cache the same way. Entries in use are never removed. The cache also keeps 1024 MiB free on its volume, or `health_check.min_free_disk_space_mb` when health checks are enabled. See [config.example.yaml](internal/pkg/config/config.example.yaml) for all options.

act/artifactcache/handler.go

@@ -10,6 +10,7 @@ import (
 	"crypto/hmac"
 	"crypto/rand"
 	"crypto/sha256"
+	"encoding/binary"
 	"encoding/hex"
 	"encoding/json/v2"
 	"errors"
@@ -78,7 +79,8 @@ type credEntry struct {
 
 type Handler struct {
 	dir      string
-	storage  *Storage
+	storage  cacheStorage
+	s3       *s3Storage
 	router   *httprouter.Router
 	listener net.Listener
 	port     int
@@ -88,6 +90,9 @@ type Handler struct {
 	gcing atomic.Bool
 	gcAt  time.Time
 
+	stopSync context.CancelFunc
+	syncing  sync.WaitGroup
+
 	outboundIP string
 
 	// internalSecret guards /_internal/{register,revoke}. When set, a remote
@@ -117,6 +122,7 @@ type Options struct {
 	Dir        string
 	OutboundIP string
 	Port       uint16
+	S3         *S3Options
 	Upstream   string
 
 	// InternalSecret, when non-empty, enables a control-plane API at
@@ -185,6 +191,12 @@ func StartHandler(opts Options) (*Handler, error) {
 		return nil, err
 	}
 	h.storage = storage
+	if opts.S3 != nil {
+		if h.s3, err = newS3Storage(storage, *opts.S3); err != nil {
+			return nil, err
+		}
+		h.storage = h.s3
+	}
 
 	secret, err := loadOrCreateSecret(dir)
 	if err != nil {
@@ -216,6 +228,11 @@ func StartHandler(opts Options) (*Handler, error) {
 	if err := h.serve(opts.Port, router); err != nil {
 		return nil, err
 	}
+	if h.s3 != nil {
+		ctx, cancel := context.WithCancel(context.Background())
+		h.stopSync = cancel
+		h.syncing.Go(func() { h.syncMetadata(ctx) })
+	}
 	return h, nil
 }
 
@@ -380,6 +397,10 @@ func (h *Handler) Close() error {
 	if h == nil {
 		return nil
 	}
+	if h.stopSync != nil {
+		h.stopSync()
+		h.syncing.Wait()
+	}
 	var retErr error
 	if h.server != nil {
 		err := h.server.Close()
@@ -413,6 +434,72 @@ func (h *Handler) openDB() (*bolthold.Store, error) {
 	})
 }
 
+// syncMetadata mirrors the bucket into the store until ctx ends, so no request waits on S3 for it.
+func (h *Handler) syncMetadata(ctx context.Context) {
+	ticker := time.NewTicker(metadataSyncInterval)
+	defer ticker.Stop()
+	for {
+		if err := h.importMetadata(ctx); err != nil && ctx.Err() == nil {
+			h.logger.Warnf("sync S3 cache: %v", err)
+		}
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+		}
+	}
+}
+
+// importMetadata lists after snapshotting the store, so an entry committed meanwhile, published before it is stored, stays.
+func (h *Handler) importMetadata(ctx context.Context) error {
+	db, err := h.openDB()
+	if err != nil {
+		return err
+	}
+	local := h.caches(db, bolthold.Where("Complete").Eq(true).Index("Complete"))
+	db.Close()
+
+	published, err := h.s3.published(ctx)
+	if err != nil {
+		return err
+	}
+	var gone []*Cache
+	for _, cache := range local {
+		if !published[cache.ID] {
+			gone = append(gone, cache)
+		}
+		delete(published, cache.ID)
+	}
+	added := make([]*Cache, 0, len(published))
+	for id := range published {
+		cache, err := h.s3.fetch(ctx, id)
+		if err != nil {
+			return err
+		}
+		added = append(added, cache)
+	}
+
+	db, err = h.openDB()
+	if err != nil {
+		return err
+	}
+	defer db.Close()
+	return db.Bolt().Update(func(tx *bbolt.Tx) error {
+		for _, cache := range added {
+			if err := db.TxUpsert(tx, cache.ID, cache); err != nil {
+				return err
+			}
+		}
+		for _, cache := range gone {
+			_ = h.s3.Storage.Remove(cache.ID) // a blob kept on disk before the runner used S3
+			if err := db.TxDelete(tx, cache.ID, cache); err != nil && !errors.Is(err, bolthold.ErrNotFound) {
+				return err
+			}
+		}
+		return nil
+	})
+}
+
 // GET /_apis/artifactcache/cache
 func (h *Handler) find(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
 	cred := credFromContext(r.Context())
@@ -455,7 +542,7 @@ func (h *Handler) lookupCache(db *bolthold.Store, repo string, keys []string, ve
 		return nil, err
 	}
 	if !ok {
-		_ = db.Delete(cache.ID, cache)
+		h.deleteCache(db, cache)
 		return nil, nil //nolint:nilnil // absence is not an error here
 	}
 	// Handing out a download URL counts as access, or eviction could drop the entry between
@@ -487,7 +574,7 @@ func (h *Handler) reserve(w http.ResponseWriter, r *http.Request, _ httprouter.P
 	now := time.Now().Unix()
 	cache.CreatedAt = now
 	cache.UsedAt = now
-	if err := insertCache(db, cache); err != nil {
+	if err := h.insertCache(db, cache); err != nil {
 		h.responseJSON(w, r, 500, err)
 		return
 	}
@@ -601,6 +688,12 @@ func (h *Handler) commitCache(cache *Cache) error {
 	cache.Size = written
 	cache.Complete = true
 	cache.UsedAt = time.Now().Unix() // a just-written entry counts as accessed, so it cannot be its own eviction victim
+	if h.s3 != nil {
+		if err := h.s3.publish(cache); err != nil {
+			_ = h.storage.Remove(cache.ID)
+			return err
+		}
+	}
 
 	db, err := h.openDB()
 	if err != nil {
@@ -610,6 +703,9 @@ func (h *Handler) commitCache(cache *Cache) error {
 	if err := db.Update(cache.ID, cache); err != nil {
 		return err
 	}
+	if h.s3 != nil {
+		return nil // lifecycle rules on the bucket bound its size
+	}
 	// A commit is the only thing that grows the store, so the only thing that can push the
 	// volume under the floor.
 	h.evictRepo(db, cache.Repo)
@@ -873,7 +969,13 @@ func findExactCache(db *bolthold.Store, repo, key, version string, complete bool
 	return cache, nil
 }
 
-func insertCache(db *bolthold.Store, cache *Cache) error {
+func (h *Handler) insertCache(db *bolthold.Store, cache *Cache) error {
+	if h.s3 != nil {
+		var id [8]byte
+		_, _ = rand.Read(id[:])
+		cache.ID = binary.BigEndian.Uint64(id[:]) >> 11 // IDs must be unique across runners, and v1 clients parse an ID as a JS number
+		return db.Insert(cache.ID, cache)
+	}
 	return db.Bolt().Update(func(tx *bbolt.Tx) error {
 		if err := db.TxInsert(tx, bolthold.NextSequence(), cache); err != nil {
 			return fmt.Errorf("insert cache: %w", err)
@@ -931,6 +1033,8 @@ const (
 	// a stale reservation.
 	uploadStallTimeout = 5 * time.Minute
 
+	metadataSyncInterval = 30 * time.Second
+
 	defaultMinFreeDisk = 1024 * miB
 )
 
@@ -978,6 +1082,9 @@ func (h *Handler) gcCache() {
 	defer db.Close()
 
 	h.evictIncomplete(db)
+	if h.s3 != nil {
+		return // lifecycle rules on the bucket expire its entries
+	}
 	h.evictExpired(db)
 	h.evictSuperseded(db)
 	h.evictOversized(db)
@@ -1175,7 +1282,11 @@ func totalSize(caches []*Cache) int64 {
 // deleteCache drops an entry and its bytes, reporting whether it went fully. The blob goes
 // first, so a failed unlink leaves the row for the next sweep instead of orphaning bytes.
 func (h *Handler) deleteCache(db *bolthold.Store, cache *Cache) bool {
-	if err := h.storage.Remove(cache.ID); err != nil {
+	storage := h.storage
+	if h.s3 != nil && !cache.Complete {
+		storage = h.s3.Storage // an upload not yet committed has nothing in the bucket
+	}
+	if err := storage.Remove(cache.ID); err != nil {
 		h.logger.Warnf("remove cache blob: %v", err)
 		return false
 	}

act/artifactcache/handler_test.go

@@ -864,7 +864,7 @@ func TestHandler_gcCache(t *testing.T) {
 	db, err := handler.openDB()
 	require.NoError(t, err)
 	for _, c := range cases {
-		require.NoError(t, insertCache(db, c.Cache))
+		require.NoError(t, handler.insertCache(db, c.Cache))
 	}
 	require.NoError(t, db.Close())
 
@@ -1036,7 +1036,7 @@ func TestHandler_SweepKeepsEntryWhenBlobSurvives(t *testing.T) {
 	handler := newTestHandler(t, Policy{Retention: testRetention}, cache)
 
 	// A non-empty directory where the blob belongs makes os.Remove fail on every platform.
-	blob := handler.storage.filename(cache.ID)
+	blob := handler.storage.(*Storage).filename(cache.ID)
 	require.NoError(t, os.MkdirAll(blob, 0o755))
 	require.NoError(t, os.WriteFile(filepath.Join(blob, "held"), []byte("x"), 0o600))
 
@@ -1119,24 +1119,28 @@ func TestHandler_touchCacheSkipsFreshCompletedEntries(t *testing.T) {
 // newTestHandler starts a handler with testToken registered, seeded with entries.
 func newTestHandler(t *testing.T, policy Policy, entries ...*Cache) *Handler {
 	t.Helper()
-	handler, err := StartHandler(Options{
-		Dir:        filepath.Join(t.TempDir(), "artifactcache"),
-		OutboundIP: "127.0.0.1",
-		Policy:     policy,
-	})
-	require.NoError(t, err)
-	t.Cleanup(func() { require.NoError(t, handler.Close()) })
-	handler.RegisterJob(testToken, JobCredential{Repo: testRepo})
+	handler := startTestHandler(t, Options{Policy: policy})
 
 	db, err := handler.openDB()
 	require.NoError(t, err)
 	for _, e := range entries {
-		require.NoError(t, insertCache(db, e))
+		require.NoError(t, handler.insertCache(db, e))
 	}
 	require.NoError(t, db.Close())
 	return handler
 }
 
+func startTestHandler(t *testing.T, opts Options) *Handler {
+	t.Helper()
+	opts.Dir = filepath.Join(t.TempDir(), "artifactcache")
+	opts.OutboundIP = "127.0.0.1"
+	handler, err := StartHandler(opts)
+	require.NoError(t, err)
+	t.Cleanup(func() { require.NoError(t, handler.Close()) })
+	handler.RegisterJob(testToken, JobCredential{Repo: testRepo})
+	return handler
+}
+
 // keptKeys reports which of entries are still in the store.
 func keptKeys(t *testing.T, handler *Handler, entries []*Cache) []string {
 	t.Helper()
@@ -1477,8 +1481,8 @@ func TestHandler_GC_PerRepoDedup(t *testing.T) {
 	stale := time.Now().Add(-inUseGrace - time.Minute).Unix()
 	a := &Cache{Repo: "owner/repoA", Key: key, Version: version, Complete: true, CreatedAt: stale, UsedAt: stale, Size: 1}
 	b := &Cache{Repo: "owner/repoB", Key: key, Version: version, Complete: true, CreatedAt: now, UsedAt: now, Size: 1}
-	require.NoError(t, insertCache(db, a))
-	require.NoError(t, insertCache(db, b))
+	require.NoError(t, handler.insertCache(db, a))
+	require.NoError(t, handler.insertCache(db, b))
 	// Write the backing blobs so the dedup deletion has something to remove.
 	require.NoError(t, handler.storage.Write(a.ID, 0, strings.NewReader("a")))
 	_, err = handler.storage.Commit(a.ID, 1)

act/artifactcache/handler_v2.go

@@ -112,7 +112,7 @@ func (h *Handler) v2CreateCacheEntry(w http.ResponseWriter, r *http.Request, _ h
 		CreatedAt: now,
 		UsedAt:    now,
 	}
-	if err := insertCache(db, cache); err != nil {
+	if err := h.insertCache(db, cache); err != nil {
 		h.twirpError(w, r, twirpInternal, err)
 		return
 	}

act/artifactcache/s3_storage.go

@@ -0,0 +1,326 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package artifactcache
+
+import (
+	"bytes"
+	"cmp"
+	"context"
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/json/v2"
+	"encoding/xml"
+	"errors"
+	"fmt"
+	"io"
+	"io/fs"
+	"maps"
+	"net/http"
+	"net/url"
+	"os"
+	"path"
+	"slices"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// S3Options configures the bucket that stores completed cache entries.
+type S3Options struct {
+	Endpoint  string
+	Region    string
+	Bucket    string
+	Prefix    string
+	PathStyle *bool // nil uses virtual-hosted requests on AWS and path-style ones elsewhere
+	AccessKey string
+	SecretKey string
+}
+
+type cacheStorage interface {
+	Exist(uint64) (bool, error)
+	Write(uint64, int64, io.Reader) error
+	WriteBlock(uint64, string, io.Reader) error
+	OrderBlocks(uint64, []string) error
+	Commit(uint64, int64) (int64, error)
+	Serve(http.ResponseWriter, *http.Request, uint64)
+	Remove(uint64) error
+}
+
+const s3PartSize = 5 << 30 // the largest part S3 accepts
+
+// s3Storage stages uploads on disk and keeps completed entries and their metadata in a bucket.
+type s3Storage struct {
+	*Storage
+	client    *http.Client
+	bucketURL *url.URL
+	opts      S3Options
+}
+
+type s3Part struct {
+	PartNumber int
+	ETag       string
+}
+
+func newS3Storage(staging *Storage, opts S3Options) (*s3Storage, error) {
+	endpoint, err := url.Parse(opts.Endpoint)
+	if err != nil || endpoint.Host == "" || (endpoint.Scheme != "http" && endpoint.Scheme != "https") {
+		return nil, fmt.Errorf("invalid S3 endpoint %q", opts.Endpoint)
+	}
+	transport, _ := http.DefaultTransport.(*http.Transport)
+	transport = transport.Clone()
+	transport.ResponseHeaderTimeout = time.Minute // a stalled endpoint must not hold the store forever
+	pathStyle := !strings.HasSuffix(endpoint.Hostname(), ".amazonaws.com")
+	if opts.PathStyle != nil {
+		pathStyle = *opts.PathStyle
+	}
+	if pathStyle {
+		endpoint.Path = "/" + opts.Bucket
+	} else {
+		endpoint.Host = opts.Bucket + "." + endpoint.Host
+		endpoint.Path = "/"
+	}
+	opts.Region = cmp.Or(opts.Region, "us-east-1")
+	return &s3Storage{Storage: staging, client: &http.Client{Transport: transport}, bucketURL: endpoint, opts: opts}, nil
+}
+
+func (s *s3Storage) blobKey(id uint64) string {
+	return path.Join(s.opts.Prefix, "blobs", strconv.FormatUint(id, 10))
+}
+
+func (s *s3Storage) metadataDir() string {
+	return path.Join(s.opts.Prefix, "metadata") + "/"
+}
+
+func (s *s3Storage) metadataKey(id uint64) string {
+	return s.metadataDir() + strconv.FormatUint(id, 10) + ".json"
+}
+
+func (s *s3Storage) url(key string, query url.Values) *url.URL {
+	u := *s.bucketURL
+	u.Path = path.Join(u.Path, key)
+	u.RawPath = strings.NewReplacer("+", "%20", "%2F", "/").Replace(url.QueryEscape(u.Path)) // SigV4 encoding
+	u.RawQuery = strings.ReplaceAll(query.Encode(), "+", "%20")
+	return &u
+}
+
+// sign authorizes req with AWS Signature Version 4, leaving the payload unsigned so bodies can stream.
+// https://docs.aws.amazon.com/AmazonS3/latest/API/sig-v4-header-based-auth.html
+func (s *s3Storage) sign(req *http.Request, now time.Time) {
+	date := now.UTC().Format("20060102T150405Z")
+	req.Header.Set("X-Amz-Date", date)
+	if req.Header.Get("X-Amz-Content-Sha256") == "" {
+		req.Header.Set("X-Amz-Content-Sha256", "UNSIGNED-PAYLOAD")
+	}
+	headers := map[string]string{"host": req.URL.Host}
+	for name, values := range req.Header {
+		if name = strings.ToLower(name); strings.HasPrefix(name, "x-amz-") {
+			headers[name] = strings.Join(values, ",")
+		}
+	}
+	names := slices.Sorted(maps.Keys(headers))
+	canonical := []string{req.Method, req.URL.EscapedPath(), req.URL.RawQuery}
+	for _, name := range names {
+		canonical = append(canonical, name+":"+headers[name])
+	}
+	canonical = append(canonical, "", strings.Join(names, ";"), req.Header.Get("X-Amz-Content-Sha256"))
+	scope := date[:8] + "/" + s.opts.Region + "/s3/aws4_request"
+	signature := []byte("AWS4" + s.opts.SecretKey)
+	for _, data := range []string{date[:8], s.opts.Region, "s3", "aws4_request", fmt.Sprintf("AWS4-HMAC-SHA256\n%s\n%s\n%x", date, scope, sha256.Sum256([]byte(strings.Join(canonical, "\n"))))} { // key derivation, the last round signs
+		mac := hmac.New(sha256.New, signature)
+		_, _ = mac.Write([]byte(data))
+		signature = mac.Sum(nil)
+	}
+	req.Header.Set("Authorization", fmt.Sprintf("AWS4-HMAC-SHA256 Credential=%s/%s,SignedHeaders=%s,Signature=%x", s.opts.AccessKey, scope, strings.Join(names, ";"), signature))
+}
+
+// do returns the response to a signed request when it succeeded, fs.ErrNotExist for a missing key.
+func (s *s3Storage) do(ctx context.Context, method, key string, query url.Values, header http.Header, body io.Reader) (*http.Response, error) {
+	var size int64
+	if sized, ok := body.(interface{ Size() int64 }); ok {
+		size = sized.Size()
+	}
+	if size == 0 {
+		body = nil
+	}
+	req, err := http.NewRequestWithContext(ctx, method, s.url(key, query).String(), body)
+	if err != nil {
+		return nil, err
+	}
+	req.ContentLength = size
+	maps.Copy(req.Header, header)
+	s.sign(req, time.Now())
+	resp, err := s.client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	if resp.StatusCode < http.StatusMultipleChoices {
+		return resp, nil
+	}
+	defer drain(resp)
+	var failure struct{ Code, Message string }
+	_ = xml.NewDecoder(resp.Body).Decode(&failure)
+	if resp.StatusCode == http.StatusNotFound && (failure.Code == "NoSuchKey" || failure.Code == "" && method == http.MethodHead) {
+		return nil, fs.ErrNotExist
+	}
+	return nil, fmt.Errorf("S3 %s %s: %s", method, key, cmp.Or(strings.TrimSpace(failure.Code+" "+failure.Message), resp.Status))
+}
+
+func (s *s3Storage) call(ctx context.Context, method, key string, query url.Values, body io.Reader, result any) (http.Header, error) {
+	resp, err := s.do(ctx, method, key, query, nil, body)
+	if err != nil {
+		return nil, err
+	}
+	defer drain(resp)
+	if result == nil {
+		return resp.Header, nil
+	}
+	return resp.Header, xml.NewDecoder(resp.Body).Decode(result)
+}
+
+// drain reads a response to its end before closing it, so its connection gets reused.
+func drain(resp *http.Response) {
+	_, _ = io.Copy(io.Discard, resp.Body)
+	_ = resp.Body.Close()
+}
+
+func (s *s3Storage) Exist(id uint64) (bool, error) {
+	_, err := s.call(context.Background(), http.MethodHead, s.blobKey(id), nil, nil, nil)
+	if errors.Is(err, fs.ErrNotExist) {
+		return false, nil
+	}
+	return err == nil, err
+}
+
+func (s *s3Storage) Commit(id uint64, size int64) (int64, error) {
+	written, err := s.Storage.Commit(id, size)
+	if err != nil {
+		return 0, err
+	}
+	defer func() { _ = s.Storage.Remove(id) }()
+	file, err := os.Open(s.filename(id))
+	if err != nil {
+		return 0, err
+	}
+	defer file.Close()
+	if err := s.upload(context.Background(), s.blobKey(id), file, written); err != nil {
+		return 0, fmt.Errorf("upload cache to S3: %w", err)
+	}
+	return written, nil
+}
+
+// upload always goes in parts, the only way S3 takes an object over 5 GiB.
+func (s *s3Storage) upload(ctx context.Context, key string, file io.ReaderAt, size int64) error {
+	var created struct {
+		UploadID string `xml:"UploadId"`
+	}
+	if _, err := s.call(ctx, http.MethodPost, key, url.Values{"uploads": {""}}, nil, &created); err != nil {
+		return err
+	}
+	var completion struct {
+		XMLName xml.Name `xml:"CompleteMultipartUpload"`
+		Parts   []s3Part `xml:"Part"`
+	}
+	for offset := int64(0); offset == 0 || offset < size; offset += s3PartSize {
+		number, length := len(completion.Parts)+1, min(s3PartSize, size-offset)
+		query := url.Values{"partNumber": {strconv.Itoa(number)}, "uploadId": {created.UploadID}}
+		header, err := s.call(ctx, http.MethodPut, key, query, io.NewSectionReader(file, offset, length), nil)
+		if err != nil {
+			return err
+		}
+		completion.Parts = append(completion.Parts, s3Part{number, header.Get("ETag")})
+	}
+	body, err := xml.Marshal(completion)
+	if err != nil {
+		return err
+	}
+	var result struct{ Code, Message string } // a completion can fail after its 200 status
+	if _, err := s.call(ctx, http.MethodPost, key, url.Values{"uploadId": {created.UploadID}}, bytes.NewReader(body), &result); err != nil {
+		return err
+	}
+	if result.Code != "" {
+		return fmt.Errorf("S3 complete upload %s: %s %s", key, result.Code, result.Message)
+	}
+	return nil
+}
+
+func (s *s3Storage) Serve(w http.ResponseWriter, r *http.Request, id uint64) {
+	header := http.Header{}
+	if byteRange := r.Header.Get("Range"); byteRange != "" {
+		header.Set("Range", byteRange)
+	}
+	resp, err := s.do(r.Context(), http.MethodGet, s.blobKey(id), nil, header, nil)
+	if errors.Is(err, fs.ErrNotExist) {
+		http.NotFound(w, r)
+		return
+	} else if err != nil {
+		http.Error(w, "read cache from S3", http.StatusBadGateway)
+		return
+	}
+	defer resp.Body.Close()
+	for _, name := range []string{"Content-Length", "Content-Range"} {
+		if value := resp.Header.Get(name); value != "" {
+			w.Header().Set(name, value)
+		}
+	}
+	w.WriteHeader(resp.StatusCode)
+	_, _ = io.Copy(w, resp.Body)
+}
+
+// Remove unpublishes an entry before deleting its blob, so no runner imports it without its bytes.
+func (s *s3Storage) Remove(id uint64) error {
+	for _, key := range []string{s.metadataKey(id), s.blobKey(id)} {
+		if _, err := s.call(context.Background(), http.MethodDelete, key, nil, nil, nil); err != nil && !errors.Is(err, fs.ErrNotExist) {
+			return fmt.Errorf("remove %s from S3: %w", key, err)
+		}
+	}
+	return s.Storage.Remove(id)
+}
+
+func (s *s3Storage) publish(cache *Cache) error {
+	data, err := json.Marshal(cache)
+	if err != nil {
+		return err
+	}
+	if _, err := s.call(context.Background(), http.MethodPut, s.metadataKey(cache.ID), nil, bytes.NewReader(data), nil); err != nil {
+		return fmt.Errorf("publish cache to S3: %w", err)
+	}
+	return nil
+}
+
+func (s *s3Storage) published(ctx context.Context) (map[uint64]bool, error) {
+	ids := make(map[uint64]bool)
+	query := url.Values{"list-type": {"2"}, "prefix": {s.metadataDir()}}
+	for {
+		var page struct {
+			Contents              []struct{ Key string }
+			IsTruncated           bool
+			NextContinuationToken string
+		}
+		if _, err := s.call(ctx, http.MethodGet, "", query, nil, &page); err != nil {
+			return nil, fmt.Errorf("list S3 cache metadata: %w", err)
+		}
+		for _, object := range page.Contents {
+			if id, err := strconv.ParseUint(strings.TrimSuffix(strings.TrimPrefix(object.Key, s.metadataDir()), ".json"), 10, 64); err == nil {
+				ids[id] = true
+			}
+		}
+		if !page.IsTruncated {
+			return ids, nil
+		}
+		query.Set("continuation-token", page.NextContinuationToken)
+	}
+}
+
+func (s *s3Storage) fetch(ctx context.Context, id uint64) (*Cache, error) {
+	resp, err := s.do(ctx, http.MethodGet, s.metadataKey(id), nil, nil, nil)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	cache := &Cache{}
+	if err := json.UnmarshalRead(resp.Body, cache); err != nil {
+		return nil, fmt.Errorf("read S3 cache metadata %d: %w", id, err)
+	}
+	return cache, nil
+}

act/artifactcache/s3_storage_test.go

@@ -0,0 +1,46 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package artifactcache
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/johannesboyne/gofakes3"
+	"github.com/johannesboyne/gofakes3/backend/s3mem"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestHandler_S3SharesEntriesAndDropsExpiredOnes(t *testing.T) {
+	backend := s3mem.New()
+	require.NoError(t, backend.CreateBucket("cache"))
+	server := httptest.NewServer(gofakes3.New(backend).Server())
+	t.Cleanup(server.Close)
+	opts := Options{S3: &S3Options{Endpoint: server.URL, Bucket: "cache", Prefix: "runners", AccessKey: "key", SecretKey: "secret"}}
+	saver, restorer := startTestHandler(t, opts), startTestHandler(t, opts)
+	entry := map[string]any{"key": "deps", "version": "v1"}
+
+	finalized, _ := saveV2(t, saver, "deps", "v1", []byte("archive"))
+	require.Equal(t, true, finalized["ok"])
+	require.NoError(t, restorer.importMetadata(t.Context()))
+	found := v2Call(t, restorer, testClient, "GetCacheEntryDownloadURL", entry)
+	require.Equal(t, true, found["ok"])
+	assert.Equal(t, []byte("archive"), getURL(t, found["signed_download_url"].(string)))
+
+	require.NoError(t, backend.ForceDeleteBucket("cache"))
+	require.NoError(t, backend.CreateBucket("cache"))
+	require.NoError(t, restorer.importMetadata(t.Context()))
+	assert.Equal(t, true, v2Call(t, restorer, testClient, "CreateCacheEntry", entry)["ok"])
+}
+
+func TestS3StorageSignsLikeAWS(t *testing.T) {
+	storage := &s3Storage{opts: S3Options{Region: "us-east-1", AccessKey: "AKIAIOSFODNN7EXAMPLE", SecretKey: "wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY"}}
+	req := httptest.NewRequest(http.MethodGet, "https://examplebucket.s3.amazonaws.com/?max-keys=2&prefix=J", nil)
+	req.Header.Set("X-Amz-Content-Sha256", "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855")
+	storage.sign(req, time.Date(2013, 5, 24, 0, 0, 0, 0, time.UTC))
+	assert.Equal(t, "AWS4-HMAC-SHA256 Credential=AKIAIOSFODNN7EXAMPLE/20130524/us-east-1/s3/aws4_request,SignedHeaders=host;x-amz-content-sha256;x-amz-date,Signature=34b48302e7b5fa45bde8084f4b7868a86f0a534bc59db6670ed5711ef69dc6f7", req.Header.Get("Authorization"))
+}

go.mod

@@ -19,6 +19,7 @@ require (
 	github.com/go-git/go-billy/v5 v5.9.1
 	github.com/go-git/go-git/v5 v5.19.2
 	github.com/google/go-cmp v0.7.0
+	github.com/johannesboyne/gofakes3 v1.2.0
 	github.com/joho/godotenv v1.5.1
 	github.com/julienschmidt/httprouter v1.3.0
 	github.com/kballard/go-shellquote v0.0.0-20180428030007-95032a82bc51
@@ -87,6 +88,7 @@ require (
 	github.com/pjbgf/sha1cd v0.6.0 // indirect
 	github.com/prometheus/common v0.70.1 // indirect
 	github.com/prometheus/procfs v0.21.1 // indirect
+	github.com/ryszard/goskiplist v0.0.0-20150312221310-2dfbae5fcf46 // indirect
 	github.com/santhosh-tekuri/jsonschema/v6 v6.0.3 // indirect
 	github.com/sergi/go-diff v1.4.0 // indirect
 	github.com/skeema/knownhosts v1.3.2 // indirect
@@ -95,7 +97,9 @@ require (
 	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
 	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.70.0 // indirect
 	go.opentelemetry.io/otel/metric v1.46.0 // indirect
+	go.shabbyrobe.org/gocovmerge v0.0.0-20230507111327-fa4f82cfbf4d // indirect
 	go.yaml.in/yaml/v3 v3.0.5 // indirect
 	golang.org/x/crypto v0.57.0 // indirect
+	golang.org/x/tools v0.49.0 // indirect
 	gopkg.in/warnings.v0 v0.1.2 // indirect
 )

go.sum

@@ -19,12 +19,40 @@ github.com/armon/go-socks5 v0.0.0-20160902184237-e75332964ef5 h1:0CwZNZbxp69SHPd
 github.com/armon/go-socks5 v0.0.0-20160902184237-e75332964ef5/go.mod h1:wHh0iHkYZB8zMSxRWpUBQtwG5a7fFgvEO+odwuTv2gs=
 github.com/avast/retry-go/v5 v5.0.0 h1:kf1Qc2UsTZ4qq8elDymqfbISvkyMuhgRxuJqX2NHP7k=
 github.com/avast/retry-go/v5 v5.0.0/go.mod h1://d+usmKWio1agtZfS1H/ltTqwtIfBnRq9zEwjc3eH8=
+github.com/aws/aws-sdk-go-v2 v1.41.5 h1:dj5kopbwUsVUVFgO4Fi5BIT3t4WyqIDjGKCangnV/yY=
+github.com/aws/aws-sdk-go-v2 v1.41.5/go.mod h1:mwsPRE8ceUUpiTgF7QmQIJ7lgsKUPQOUl3o72QBrE1o=
+github.com/aws/aws-sdk-go-v2/aws/protocol/eventstream v1.7.8 h1:eBMB84YGghSocM7PsjmmPffTa+1FBUeNvGvFou6V/4o=
+github.com/aws/aws-sdk-go-v2/aws/protocol/eventstream v1.7.8/go.mod h1:lyw7GFp3qENLh7kwzf7iMzAxDn+NzjXEAGjKS2UOKqI=
+github.com/aws/aws-sdk-go-v2/credentials v1.17.67 h1:9KxtdcIA/5xPNQyZRgUSpYOE6j9Bc4+D7nZua0KGYOM=
+github.com/aws/aws-sdk-go-v2/credentials v1.17.67/go.mod h1:p3C44m+cfnbv763s52gCqrjaqyPikj9Sg47kUVaNZQQ=
+github.com/aws/aws-sdk-go-v2/feature/s3/manager v1.17.75 h1:S61/E3N01oral6B3y9hZ2E1iFDqCZPPOBoBQretCnBI=
+github.com/aws/aws-sdk-go-v2/feature/s3/manager v1.17.75/go.mod h1:bDMQbkI1vJbNjnvJYpPTSNYBkI/VIv18ngWb/K84tkk=
+github.com/aws/aws-sdk-go-v2/internal/configsources v1.4.21 h1:Rgg6wvjjtX8bNHcvi9OnXWwcE0a2vGpbwmtICOsvcf4=
+github.com/aws/aws-sdk-go-v2/internal/configsources v1.4.21/go.mod h1:A/kJFst/nm//cyqonihbdpQZwiUhhzpqTsdbhDdRF9c=
+github.com/aws/aws-sdk-go-v2/internal/endpoints/v2 v2.7.21 h1:PEgGVtPoB6NTpPrBgqSE5hE/o47Ij9qk/SEZFbUOe9A=
+github.com/aws/aws-sdk-go-v2/internal/endpoints/v2 v2.7.21/go.mod h1:p+hz+PRAYlY3zcpJhPwXlLC4C+kqn70WIHwnzAfs6ps=
+github.com/aws/aws-sdk-go-v2/internal/v4a v1.4.22 h1:rWyie/PxDRIdhNf4DzRk0lvjVOqFJuNnO8WwaIRVxzQ=
+github.com/aws/aws-sdk-go-v2/internal/v4a v1.4.22/go.mod h1:zd/JsJ4P7oGfUhXn1VyLqaRZwPmZwg44Jf2dS84Dm3Y=
+github.com/aws/aws-sdk-go-v2/service/internal/accept-encoding v1.13.7 h1:5EniKhLZe4xzL7a+fU3C2tfUN4nWIqlLesfrjkuPFTY=
+github.com/aws/aws-sdk-go-v2/service/internal/accept-encoding v1.13.7/go.mod h1:x0nZssQ3qZSnIcePWLvcoFisRXJzcTVvYpAAdYX8+GI=
+github.com/aws/aws-sdk-go-v2/service/internal/checksum v1.9.13 h1:JRaIgADQS/U6uXDqlPiefP32yXTda7Kqfx+LgspooZM=
+github.com/aws/aws-sdk-go-v2/service/internal/checksum v1.9.13/go.mod h1:CEuVn5WqOMilYl+tbccq8+N2ieCy0gVn3OtRb0vBNNM=
+github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.13.21 h1:c31//R3xgIJMSC8S6hEVq+38DcvUlgFY0FM6mSI5oto=
+github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.13.21/go.mod h1:r6+pf23ouCB718FUxaqzZdbpYFyDtehyZcmP5KL9FkA=
+github.com/aws/aws-sdk-go-v2/service/internal/s3shared v1.19.21 h1:ZlvrNcHSFFWURB8avufQq9gFsheUgjVD9536obIknfM=
+github.com/aws/aws-sdk-go-v2/service/internal/s3shared v1.19.21/go.mod h1:cv3TNhVrssKR0O/xxLJVRfd2oazSnZnkUeTf6ctUwfQ=
+github.com/aws/aws-sdk-go-v2/service/s3 v1.97.3 h1:HwxWTbTrIHm5qY+CAEur0s/figc3qwvLWsNkF4RPToo=
+github.com/aws/aws-sdk-go-v2/service/s3 v1.97.3/go.mod h1:uoA43SdFwacedBfSgfFSjjCvYe8aYBS7EnU5GZ/YKMM=
+github.com/aws/smithy-go v1.24.2 h1:FzA3bu/nt/vDvmnkg+R8Xl46gmzEDam6mZ1hzmwXFng=
+github.com/aws/smithy-go v1.24.2/go.mod h1:YE2RhdIuDbA5E5bTdciG9KrW3+TiEONeUWCqxX9i1Fc=
 github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
 github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
 github.com/bmatcuk/doublestar/v4 v4.10.0 h1:zU9WiOla1YA122oLM6i4EXvGW62DvKZVxIe6TYWexEs=
 github.com/bmatcuk/doublestar/v4 v4.10.0/go.mod h1:xBQ8jztBU6kakFMg+8WGxn0c6z1fTSPVIjEY1Wr7jzc=
 github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
 github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
+github.com/cevatbarisyilmaz/ara v0.0.4 h1:SGH10hXpBJhhTlObuZzTuFn1rrdmjQImITXnZVPSodc=
+github.com/cevatbarisyilmaz/ara v0.0.4/go.mod h1:BfFOxnUd6Mj6xmcvRxHN3Sr21Z1T3U2MYkYOmoQe4Ts=
 github.com/cloudflare/circl v1.6.5 h1:O64F26HEqNhznd/hrC5KZXVKYuKM2rx4deZDTc4ihQA=
 github.com/cloudflare/circl v1.6.5/go.mod h1:h5LNyxAc5nTue9DS5jT+48en2PSDYt3zdGnz5OstK6c=
 github.com/containerd/errdefs v1.0.0 h1:tg5yIfIlQIrxYtu9ajqY42W3lpS19XqdxRQeEwYG8PI=
@@ -87,6 +115,8 @@ github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2
 github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
 github.com/jbenet/go-context v0.0.0-20150711004518-d14ea06fba99 h1:BQSFePA1RWJOlocH6Fxy8MmwDt+yVQYULKfN0RoTN8A=
 github.com/jbenet/go-context v0.0.0-20150711004518-d14ea06fba99/go.mod h1:1lJo3i6rXxKeerYnT8Nvf0QmHCRC1n8sfWVwXF2Frvo=
+github.com/johannesboyne/gofakes3 v1.2.0 h1:I9VEzPWvvAUAGzDlhYFoZjF0AXMlkcEyZlmBwiI6Oms=
+github.com/johannesboyne/gofakes3 v1.2.0/go.mod h1:UHhRZRod9rENGFrUWTYnQHZqlNgSmjOq8DaD/ATQYRM=
 github.com/joho/godotenv v1.5.1 h1:7eLL/+HRGLY0ldzfGMeQkb7vMd0as4CfYvUVzLqw0N0=
 github.com/joho/godotenv v1.5.1/go.mod h1:f4LDr5Voq0i2e/R5DDNOoa2zzDfwtkZa6DnEwAbqwq4=
 github.com/julienschmidt/httprouter v1.3.0 h1:U0609e9tgbseu3rBINet9P48AI/D3oJs4dN7jwJOQ1U=
@@ -156,6 +186,8 @@ github.com/prometheus/procfs v0.21.1/go.mod h1:aB55Cww9pdSJVHk0hUf0inxWyyjPogFIj
 github.com/rogpeppe/go-internal v1.14.1 h1:UQB4HGPB6osV0SQTLymcB4TgvyWu6ZyliaW0tI/otEQ=
 github.com/rogpeppe/go-internal v1.14.1/go.mod h1:MaRKkUm5W0goXpeCfT7UZI6fk/L7L7so1lCWt35ZSgc=
 github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
+github.com/ryszard/goskiplist v0.0.0-20150312221310-2dfbae5fcf46 h1:GHRpF1pTW19a8tTFrMLUcfWwyC0pnifVo2ClaLq+hP8=
+github.com/ryszard/goskiplist v0.0.0-20150312221310-2dfbae5fcf46/go.mod h1:uAQ5PCi+MFsC7HjREoAz1BU+Mq60+05gifQSsHSDG/8=
 github.com/santhosh-tekuri/jsonschema/v6 v6.0.3 h1:1EYB5IzjZawrrnELUi78f9fPu57HuXjmddZPjrls/28=
 github.com/santhosh-tekuri/jsonschema/v6 v6.0.3/go.mod h1:JXeL+ps8p7/KNMjDQk3TCwPpBy0wYklyWTfbkIzdIFU=
 github.com/sergi/go-diff v1.4.0 h1:n/SP9D5ad1fORl+llWyN+D6qoUETXNZARKjyY2/KVCw=
@@ -165,6 +197,8 @@ github.com/sirupsen/logrus v1.10.2 h1:G2SED73/qrAu6YwbdxOD6peLkCBI3z7L+ykJFTXJBB
 github.com/sirupsen/logrus v1.10.2/go.mod h1:SLEg8TqYulVKKfIGHldVp2K2aYz2DKSVBq4g/H5bR7Q=
 github.com/skeema/knownhosts v1.3.2 h1:EDL9mgf4NzwMXCTfaxSD/o/a5fxDw/xL9nkU28JjdBg=
 github.com/skeema/knownhosts v1.3.2/go.mod h1:bEg3iQAuw+jyiw+484wwFJoKSLwcfd7fqRy+N0QTiow=
+github.com/spf13/afero v1.2.1 h1:qgMbHoJbPbw579P+1zVY+6n4nIFuIchaIjzZ/I/Yq8M=
+github.com/spf13/afero v1.2.1/go.mod h1:9ZxEEn6pIJ8Rxe320qSDBk6AsU0r9pR7Q4OcevTdifk=
 github.com/spf13/cobra v1.10.2 h1:DMTTonx5m65Ic0GOoRY2c16WCbHxOOw6xxezuLaBpcU=
 github.com/spf13/cobra v1.10.2/go.mod h1:7C1pvHqHw5A4vrJfjNwvOdzYu0Gml16OCs2GRiTUUS4=
 github.com/spf13/pflag v1.0.9/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
@@ -208,6 +242,8 @@ go.opentelemetry.io/otel/trace v1.46.0 h1:OULy7ccdJnZtJ0UDYFOIGaCmiWzJ8Vi2G/Rsu6
 go.opentelemetry.io/otel/trace v1.46.0/go.mod h1:J7GAXweO77XSFkB/rmAqk9D6ihszhFjLU+d9WuUxDLI=
 go.opentelemetry.io/proto/otlp v1.11.0 h1:5rrYs0Ykyj50sdU/JU0x8etU+LubXWb+gED6TbEdMIk=
 go.opentelemetry.io/proto/otlp v1.11.0/go.mod h1:SmVizdCOAm3XBtG1g1NnOdhW6jtddT72hLMhv8VwA8E=
+go.shabbyrobe.org/gocovmerge v0.0.0-20230507111327-fa4f82cfbf4d h1:Ns9kd1Rwzw7t0BR8XMphenji4SmIoNZPn8zhYmaVKP8=
+go.shabbyrobe.org/gocovmerge v0.0.0-20230507111327-fa4f82cfbf4d/go.mod h1:92Uoe3l++MlthCm+koNi0tcUCX3anayogF0Pa/sp24k=
 go.uber.org/goleak v1.3.0 h1:2K3zAYmnTNqV73imy9J1T3WC+gmCePx2hEGkimedGto=
 go.uber.org/goleak v1.3.0/go.mod h1:CoHD4mav9JJNrW/WLlf7HGZPjdw8EucARQHekz1X6bE=
 go.yaml.in/yaml/v2 v2.4.4 h1:tuyd0P+2Ont/d6e2rl3be67goVK4R6deVxCUX5vyPaQ=
@@ -244,12 +280,16 @@ golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
 golang.org/x/text v0.42.0 h1:JbOZXgfeCPU9gacVtYliJqOhD+zhrEqK4LfdpmlUZqI=
 golang.org/x/text v0.42.0/go.mod h1:ojzP1Z+2QtioaF8DTtO8K5q7JWVVYwZKenzujK0Zd0E=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
+golang.org/x/tools v0.49.0 h1:3NI7VXzL9+1WZD52Dx2ttoPwD5DWrFGpl9mFZDlmisI=
+golang.org/x/tools v0.49.0/go.mod h1:SJNXV9DBKT0UbdttsQjbfJlAE/q+y36++zo3uL3N0Oo=
 google.golang.org/protobuf v1.36.12 h1:pJOKDDOyeXErUroCihFAd5LQuwXBSpVnKGrj5o/fwxc=
 google.golang.org/protobuf v1.36.12/go.mod h1:HTf+CrKn2C3g5S8VImy6tdcUvCska2kB7j23XfzDpco=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
 gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=
+gopkg.in/mgo.v2 v2.0.0-20180705113604-9856a29383ce h1:xcEWjVhvbDy+nHP67nPDDpbYrY+ILlfndk4bRioVHaU=
+gopkg.in/mgo.v2 v2.0.0-20180705113604-9856a29383ce/go.mod h1:yeKp02qBN3iKW1OzL3MGk2IdtZzaj7SFntXj72NppTA=
 gopkg.in/warnings.v0 v0.1.2 h1:wFXVbFY8DY5/xOe1ECiWdKCzZlxgshcYVNkBHstARME=
 gopkg.in/warnings.v0 v0.1.2/go.mod h1:jksf8JmL6Qr/oQM2OXTHunEvvTAsrWBLb6OOjuVWRNI=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=

internal/app/cmd/cache-server.go

@@ -29,6 +29,9 @@ func runCacheServer(configFile *string, cacheArgs *cacheServerArgs) func(cmd *co
 		}
 
 		initLogging(cfg)
+		if cfg.Cache.S3 != nil {
+			return errors.New("cache-server does not support cache.s3; set cache.s3 on the runners instead")
+		}
 
 		var (
 			dir  = cfg.Cache.Dir

internal/app/run/runner.go

@@ -98,15 +98,14 @@ func NewRunner(cfg *config.Config, reg *config.Registration, cli client.Client)
 	maps.Copy(envs, cfg.Runner.Envs)
 	var cacheHandler *artifactcache.Handler
 	if cacheEnabled(cfg) {
-		if cfg.Cache.ExternalServer != "" {
-			warnIgnoredCachePolicy(cfg)
-		}
+		warnIgnoredCachePolicy(cfg)
 		warnIgnoredCacheSecret(cfg)
 		handler, err := artifactcache.StartHandler(artifactcache.Options{
 			Dir:        cfg.Cache.Dir,
 			OutboundIP: cfg.Cache.Host,
 			Port:       cfg.Cache.Port,
 			Upstream:   cfg.Cache.ExternalServer,
+			S3:         cacheS3(cfg),
 			Policy:     CachePolicy(cfg),
 			Logger:     log.StandardLogger().WithField("module", "cache_request"),
 		})
@@ -804,12 +803,27 @@ func CachePolicy(cfg *config.Config) artifactcache.Policy {
 	}
 }
 
-// warnIgnoredCachePolicy flags eviction settings configured on a runner that points at an external cache server.
+func cacheS3(cfg *config.Config) *artifactcache.S3Options {
+	s3 := cfg.Cache.S3
+	if s3 == nil {
+		return nil
+	}
+	return &artifactcache.S3Options{
+		Endpoint: s3.Endpoint, Region: s3.Region, Bucket: s3.Bucket, Prefix: s3.Prefix,
+		PathStyle: s3.PathStyle, AccessKey: s3.AccessKey, SecretKey: s3.SecretKey,
+	}
+}
+
+// warnIgnoredCachePolicy flags eviction settings configured on a runner that does not apply them.
 func warnIgnoredCachePolicy(cfg *config.Config) {
 	defaults := config.DefaultCache()
-	if cfg.Cache.Retention != defaults.Retention || cfg.Cache.RepoSizeLimit != defaults.RepoSizeLimit ||
-		cfg.Cache.SizeLimit != defaults.SizeLimit || cfg.Cache.SweepInterval != defaults.SweepInterval {
+	limits := cfg.Cache.Retention != defaults.Retention || cfg.Cache.RepoSizeLimit != defaults.RepoSizeLimit ||
+		cfg.Cache.SizeLimit != defaults.SizeLimit
+	switch {
+	case cfg.Cache.ExternalServer != "" && (limits || cfg.Cache.SweepInterval != defaults.SweepInterval):
 		log.Warn("cache eviction settings are ignored when cache.external_server is set; configure them on that server instead")
+	case cfg.Cache.S3 != nil && limits:
+		log.Warn("cache eviction settings are ignored when cache.s3 is set; use lifecycle rules on the bucket instead")
 	}
 }
 

internal/pkg/config/config.example.yaml

@@ -166,6 +166,19 @@ cache:
   # Surrounding whitespace is trimmed, so a trailing newline in the file is fine.
   # Setting both external_secret and external_secret_file is an error.
   #external_secret_file: ""
+  # Store the cache in an S3-compatible bucket such as AWS S3, MinIO or RustFS. Runners with
+  # the same settings use the same cache. Cannot be combined with external_server. Add lifecycle
+  # rules to the bucket that expire old caches and abort incomplete multipart uploads.
+  # region defaults to us-east-1, and path_style to false for AWS and true otherwise.
+  # access_key and secret_key can also be set directly instead of read from files.
+  #s3:
+  #  endpoint: "http://minio:9000"
+  #  region: "us-east-1"
+  #  bucket: "runner-cache"
+  #  prefix: "gitea-runner-cache"
+  #  path_style: true
+  #  access_key_file: "/run/secrets/cache-s3-access-key"
+  #  secret_key_file: "/run/secrets/cache-s3-secret-key"
   # When true, reuse a cached action instead of fetching from the remote on every job.
   # A moved tag (e.g. a re-tagged "v6") or an updated branch stays at the cached commit
   # until its cache entry expires or is manually removed.
@@ -176,8 +189,8 @@ cache:
   # advertised. A bundle that does not match is left alone. With v2, artifact uploads go via the
   # cache server.
   #v2: true
-  # How the cache server discards entries, ignored when external_server is set since that
-  # server applies its own. Leave a setting out for its default; 0s or 0 turns the three
+  # How the cache server discards entries, ignored when external_server or s3 is set since
+  # those apply their own. Leave a setting out for its default; 0s or 0 turns the three
   # limits off. Sizes accept 10GB, 512mb, 1TiB or a plain byte count, binary either way.
   # Whatever these allow, the cache still sheds entries to keep free space on its volume
   # above health_check.min_free_disk_space_mb when health checks are enabled.

internal/pkg/config/config.go

@@ -101,13 +101,28 @@ type Cache struct {
 	OfflineMode        bool   `yaml:"offline_mode"`         // OfflineMode reuses a cached action without fetching from the remote; a moved tag or branch stays at the cached commit until the cache entry is removed.
 	V2                 *bool  `yaml:"v2"`                   // V2 advertises the actions cache service v2 API to jobs. The bundle edit that reaches it is made either way, the artifact actions need it too. Unset means enabled.
 
-	// Eviction settings, ignored when ExternalServer is set since that server applies its own.
+	S3 *CacheS3 `yaml:"s3"` // S3 stores the cache in an S3-compatible bucket, so runners with the same settings use the same cache.
+
+	// Eviction settings, ignored when ExternalServer is set since that server applies its own. With S3, bucket lifecycle rules replace all but SweepInterval.
 	Retention     time.Duration `yaml:"retention"`       // Retention removes entries nothing has read or written within this window. Default 168h, 0 keeps them regardless of age.
 	RepoSizeLimit Size          `yaml:"repo_size_limit"` // RepoSizeLimit caps one repository, evicting least recently accessed first. Default 10GB, 0 is no limit.
 	SizeLimit     Size          `yaml:"size_limit"`      // SizeLimit caps the whole cache the same way. No limit by default.
 	SweepInterval time.Duration `yaml:"sweep_interval"`  // SweepInterval is the minimum time between two eviction sweeps. Default 1h; a cadence has no "off".
 }
 
+// CacheS3 is an S3-compatible bucket that stores the cache.
+type CacheS3 struct {
+	Endpoint      string `yaml:"endpoint"`
+	Region        string `yaml:"region"`
+	Bucket        string `yaml:"bucket"`
+	Prefix        string `yaml:"prefix"`
+	PathStyle     *bool  `yaml:"path_style"`
+	AccessKey     string `yaml:"access_key"`
+	AccessKeyFile string `yaml:"access_key_file"`
+	SecretKey     string `yaml:"secret_key"`
+	SecretKeyFile string `yaml:"secret_key_file"`
+}
+
 // DefaultCache returns the cache eviction defaults, seeded before the file is read so a
 // written 0 can mean off. SizeLimit stays zero: the free space floor bounds the whole cache.
 func DefaultCache() Cache {
@@ -266,7 +281,7 @@ func LoadDefault(file string) (*Config, error) {
 		cfg.Cache.Enabled = &b
 	}
 	// Resolved regardless of cache.enabled, because the `cache-server` command reads the secret from the same key without checking cache.enabled.
-	if err := resolveCacheExternalSecret(cfg); err != nil {
+	if err := resolveSecretFile("cache.external_secret", &cfg.Cache.ExternalSecret, cfg.Cache.ExternalSecretFile); err != nil {
 		return nil, err
 	}
 	if *cfg.Cache.Enabled {
@@ -280,6 +295,9 @@ func LoadDefault(file string) (*Config, error) {
 		if cfg.Cache.ExternalServer != "" && cfg.Cache.ExternalSecret == "" {
 			return nil, errors.New("cache.external_server is set but no shared secret is configured; set cache.external_secret (or cache.external_secret_file) to the same value used by the gitea-runner cache-server")
 		}
+		if err := resolveCacheS3(&cfg.Cache); err != nil {
+			return nil, err
+		}
 	}
 	if cfg.Container.WorkdirParent == "" {
 		cfg.Container.WorkdirParent = "workspace"
@@ -426,23 +444,44 @@ func definedRunnerConfigKeys(content []byte) (map[string]bool, error) {
 	return defined, nil
 }
 
-// resolveCacheExternalSecret loads cache.external_secret from the file named by cache.external_secret_file,
-// so deployments can mount the secret instead of committing it to the config file.
-func resolveCacheExternalSecret(cfg *Config) error {
-	if cfg.Cache.ExternalSecretFile == "" {
+// resolveSecretFile reads key from key_file, so deployments can mount a secret instead of committing it.
+func resolveSecretFile(key string, secret *string, file string) error {
+	if file == "" {
 		return nil
 	}
-	if cfg.Cache.ExternalSecret != "" {
-		return errors.New("cache.external_secret and cache.external_secret_file are both set; configure only one of them")
+	if *secret != "" {
+		return fmt.Errorf("%s and %s_file are both set; configure only one of them", key, key)
 	}
-	content, err := os.ReadFile(cfg.Cache.ExternalSecretFile)
+	content, err := os.ReadFile(file)
 	if err != nil {
-		return fmt.Errorf("read cache.external_secret_file %q: %w", cfg.Cache.ExternalSecretFile, err)
+		return fmt.Errorf("read %s_file %q: %w", key, file, err)
 	}
-	secret := strings.TrimSpace(string(content))
-	if secret == "" {
-		return fmt.Errorf("cache.external_secret_file %q contains no secret", cfg.Cache.ExternalSecretFile)
+	*secret = strings.TrimSpace(string(content))
+	if *secret == "" {
+		return fmt.Errorf("%s_file %q contains no secret", key, file)
 	}
-	cfg.Cache.ExternalSecret = secret
+	return nil
+}
+
+func resolveCacheS3(cache *Cache) error {
+	s3 := cache.S3
+	switch {
+	case s3 == nil:
+		return nil
+	case cache.ExternalServer != "":
+		return errors.New("cache.s3 and cache.external_server cannot both be set")
+	case s3.Endpoint == "" || s3.Bucket == "":
+		return errors.New("cache.s3.endpoint and cache.s3.bucket must be set")
+	}
+	if err := resolveSecretFile("cache.s3.access_key", &s3.AccessKey, s3.AccessKeyFile); err != nil {
+		return err
+	}
+	if err := resolveSecretFile("cache.s3.secret_key", &s3.SecretKey, s3.SecretKeyFile); err != nil {
+		return err
+	}
+	if s3.AccessKey == "" || s3.SecretKey == "" {
+		return errors.New("cache.s3.access_key (or cache.s3.access_key_file) and cache.s3.secret_key (or cache.s3.secret_key_file) must be set")
+	}
+	s3.Prefix = strings.Trim(s3.Prefix, "/")
 	return nil
 }

internal/pkg/config/config_test.go

@@ -42,6 +42,36 @@ cache:
 	require.NoError(t, err)
 }
 
+func TestLoadDefault_CacheS3(t *testing.T) {
+	dir := t.TempDir()
+	accessPath := filepath.Join(dir, "access.key")
+	require.NoError(t, os.WriteFile(accessPath, []byte("access\n"), 0o600))
+	path := filepath.Join(dir, "config.yaml")
+	content := `
+cache:
+  s3:
+    endpoint: "http://minio:9000"
+    bucket: "caches"
+    prefix: "/runners/"
+    access_key_file: "` + accessPath + `"
+    secret_key: "secret"
+`
+	require.NoError(t, os.WriteFile(path, []byte(content), 0o600))
+
+	cfg, err := LoadDefault(path)
+	require.NoError(t, err)
+	assert.Equal(t, CacheS3{
+		Endpoint: "http://minio:9000", Bucket: "caches", Prefix: "runners",
+		AccessKey: "access", AccessKeyFile: accessPath, SecretKey: "secret",
+	}, *cfg.Cache.S3)
+
+	require.NoError(t, os.WriteFile(path, []byte(content+`  external_server: "http://cache.invalid/"
+  external_secret: "shh"
+`), 0o600))
+	_, err = LoadDefault(path)
+	assert.ErrorContains(t, err, "cache.s3 and cache.external_server cannot both be set")
+}
+
 func TestLoadDefault_ToolCacheMode(t *testing.T) {
 	cfg, err := LoadDefault("")
 	require.NoError(t, err)