docs: explain labels, the docker image cache volume, and the dind-rootless UID (#1086)

Fixes #106
Fixes #570
Fixes #627

Reviewed-on: https://gitea.com/gitea/runner/pulls/1086
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>

examples/kubernetes/README.md

@@ -6,6 +6,11 @@ NOTE: `dind-docker.yaml` uses the native sidecar pattern (init container with `r
 
 NOTE: A helm chart for `gitea-runner` also exists for easier deployments https://gitea.com/gitea/helm-actions
 
+Each example persists **two** things, and it is worth knowing which is which:
+
+- `/data` is the runner's working directory. It holds the `.runner` registration file and, optionally, the config file — so the runner re-attaches to the server instead of registering again.
+- The Docker daemon's data root holds the images pulled for jobs (`/var/lib/docker` for the dind sidecar, `/home/rootless/.local/share/docker` for `dind-rootless`). It is *not* under `/data`. If you drop this volume, the examples still work, but the image cache is discarded whenever the pod is recreated and every job re-pulls its images.
+
 Files in this directory:
 
 - [`dind-docker.yaml`](dind-docker.yaml)

examples/kubernetes/dind-docker.yaml

@@ -1,3 +1,5 @@
+# Holds the runner's working directory (/data): the .runner registration file
+# and, optionally, the config file.
 kind: PersistentVolumeClaim
 apiVersion: v1
 metadata:
@@ -10,6 +12,21 @@ spec:
       storage: 1Gi
   storageClassName: standard
 ---
+# Holds the Docker daemon's data root (/var/lib/docker), i.e. the images pulled
+# for jobs. Without it, the image cache is lost whenever the pod is recreated
+# and every job re-pulls its images. Size it for the images you expect to cache.
+kind: PersistentVolumeClaim
+apiVersion: v1
+metadata:
+  name: docker-vol
+spec:
+  accessModes:
+  - ReadWriteOnce
+  resources:
+    requests:
+      storage: 20Gi
+  storageClassName: standard
+---
 apiVersion: v1
 data:
   # The registration token can be obtained from the web UI, API or command-line.
@@ -45,6 +62,9 @@ spec:
       - name: runner-data
         persistentVolumeClaim:
           claimName: runner-vol
+      - name: docker-data
+        persistentVolumeClaim:
+          claimName: docker-vol
       initContainers:
       - name: docker
         image: docker:28.2.2-dind
@@ -53,6 +73,8 @@ spec:
         volumeMounts:
         - name: docker-socket
           mountPath: /var/run
+        - name: docker-data
+          mountPath: /var/lib/docker
         startupProbe:
           exec:
             command: ["/usr/bin/test", "-S", "/var/run/docker.sock"]

examples/kubernetes/rootless-docker.yaml

@@ -1,3 +1,5 @@
+# Holds the runner's working directory (/data): the .runner registration file
+# and, optionally, the config file.
 kind: PersistentVolumeClaim
 apiVersion: v1
 metadata:
@@ -10,6 +12,21 @@ spec:
       storage: 1Gi
   storageClassName: standard
 ---
+# Holds the rootless Docker daemon's data root, i.e. the images pulled for jobs.
+# Without it, the image cache is lost whenever the pod is recreated and every job
+# re-pulls its images. Size it for the images you expect to cache.
+kind: PersistentVolumeClaim
+apiVersion: v1
+metadata:
+  name: docker-vol
+spec:
+  accessModes:
+  - ReadWriteOnce
+  resources:
+    requests:
+      storage: 20Gi
+  storageClassName: standard
+---
 apiVersion: v1
 data:
   # The registration token can be obtained from the web UI, API or command-line.
@@ -43,7 +60,12 @@ spec:
       - name: runner-data
         persistentVolumeClaim:
           claimName: runner-vol
+      - name: docker-data
+        persistentVolumeClaim:
+          claimName: docker-vol
       securityContext:
+        # The dind-rootless image runs as the `rootless` user (UID/GID 1000);
+        # fsGroup makes both volumes writable for it.
         fsGroup: 1000
       containers:
       - name: runner
@@ -68,4 +90,7 @@ spec:
         volumeMounts:
         - name: runner-data
           mountPath: /data
+        # The rootless daemon keeps its images here, not under /data.
+        - name: docker-data
+          mountPath: /home/rootless/.local/share/docker
 

examples/kubernetes/statefulset-dind.yaml

@@ -44,6 +44,10 @@ spec:
         volumeMounts:
         - name: docker-socket
           mountPath: /var/run
+        # Keeps the images pulled for jobs across restarts. Without this, the
+        # daemon's data root is ephemeral and every job re-pulls its images.
+        - name: docker-data
+          mountPath: /var/lib/docker
         startupProbe:
           exec:
             command: ["/usr/bin/test", "-S", "/var/run/docker.sock"]
@@ -68,6 +72,8 @@ spec:
         - name: docker-socket
           mountPath: /var/run
   volumeClaimTemplates:
+  # The runner's working directory: the .runner registration file and, optionally,
+  # the config file.
   - metadata:
       name: runner-data
     spec:
@@ -77,3 +83,14 @@ spec:
         requests:
           storage: 1Gi
       storageClassName: standard
+  # The Docker daemon's data root: the images pulled for jobs. Size it for the
+  # images you expect to cache.
+  - metadata:
+      name: docker-data
+    spec:
+      accessModes:
+      - ReadWriteOnce
+      resources:
+        requests:
+          storage: 20Gi
+      storageClassName: standard