Radicale on GKE Autopilot
Radicale is an open-source, self-hosted CalDAV/CardDAV server for calendar and contacts sync — a lightweight, pure-Python WSGI application with no framework and no database. It stores every calendar and address book as plain iCalendar/vCard files on disk. This module deploys Radicale on GKE Autopilot on top of the App_GKE foundation, which provisions and manages the shared Google Cloud and Kubernetes infrastructure.
This guide focuses on the cloud services Radicale uses and how to explore and operate them from the Google Cloud Console and the command line. For the mechanics common to every GKE application — Workload Identity, ingress, autoscaling, CI/CD, Cloud Armor, IAP, Binary Authorization, VPC Service Controls, backups, and the deployment lifecycle — refer to the App_GKE foundation guide rather than repeating them here.
1. Overview
Radicale runs as a single Python WSGI pod. The deployment wires together a small, focused set of Google Cloud services:
| Capability | Google Cloud service | Notes |
|---|---|---|
| Compute | GKE Autopilot | Single Python process pod, 1 vCPU / 1 GiB by default |
| Database | none | Radicale stores every collection as plain files — no Cloud SQL instance is created |
| Object storage | Cloud Storage, or a block PVC | storage GCS bucket by default; stateful_pvc_enabled = true swaps in a real block PVC (recommended for production) |
| Cache & queue | none | Radicale has no Redis or queue dependency |
| Secrets | Secret Manager | A real generated ADMIN_PASSWORD — Radicale ships with no default admin account at all |
| Ingress | Cloud Load Balancing | External LoadBalancer, optional custom domain + managed certificate |
Sensible defaults worth knowing up front:
- No database of any kind.
Radicale_Commonfixesdatabase_type = "NONE"— Radicale is a pure filesystem store. - Custom, thin-wrapper build.
Radicale_Commonlayers a cloud entrypoint onto the officialghcr.io/kozea/radicaleimage via Cloud Build, then mirrors the result into Artifact Registry. - Block-storage PVC recommended. Set
stateful_pvc_enabled = true(auto- resolvesworkload_typetoStatefulSet) so Radicale's collections filesystem gets real POSIX file locking, which GCS FUSE does not reliably support.stateful_pvc_storage_classdefaults tostandard(HDD) rather than SSD — collections are small text files with no high-IOPS need. - No default admin account — a real generated secret.
Radicale_Commongenerates and injects a realADMIN_PASSWORDon every deployment (see the Common guide). max_instance_countpinned to1,min_instance_countdefaults to0. Radicale's storage backend is not designed for concurrent multi-instance access, but has no database/index to warm at boot, so scale-to-zero is safe and fast.- MKCOL works natively here — but the seed job may not reach a PVC. GKE's
plain L4 LoadBalancer Service has no MKCOL restriction (unlike Cloud Run),
but with
stateful_pvc_enabled = truethe default seed job's pre-created collections may not appear — see §3.
2. Google Cloud Services & How to Explore Them
All commands assume you have run
gcloud container clusters get-credentials <cluster> --region <region> --project <project>
and that PROJECT, REGION, and NAMESPACE are set.
A. GKE Autopilot — the Radicale workload
- CLI:
kubectl get pods,svc -n "$NAMESPACE"
kubectl logs -n "$NAMESPACE" deploy/<service-name> --tail=100 # Deployment mode
kubectl logs -n "$NAMESPACE" statefulset/<service-name> --tail=100 # StatefulSet mode
B. Storage — Cloud Storage or a block PVC
- CLI:
gcloud storage buckets list --project "$PROJECT" --filter="name~radicale"
kubectl get pvc -n "$NAMESPACE" # only when stateful_pvc_enabled = true
C. Secret Manager
- CLI:
gcloud secrets list --project "$PROJECT" --filter="name~radicale"
gcloud secrets versions access latest --secret=<secret-name> --project "$PROJECT"
D. Networking & ingress
- CLI:
kubectl get svc -n "$NAMESPACE" -o wide
E. Cloud Logging & Monitoring
- CLI:
kubectl logs -n "$NAMESPACE" deploy/<service-name> --tail=100 -f
3. Radicale Application Behaviour
- No first-deploy database setup. There is no
db-initjob — Radicale has no database to bootstrap. seed-default-collectionsruns at deploy time. A one-shot initialization Job (execute_on_apply = true) writes a "Default Calendar" and "Default Address Book" directly onto the storage volume for the admin user.- No default admin account. Radicale's auth defaults to
denyalluntil an htpasswd file exists.Radicale_Commongenerates a realADMIN_PASSWORDand the cloud entrypoint writes both the INI config and a bcrypt htpasswd entry on every pod boot. - Health path. Startup and liveness probes target
/. - Inspect job execution:
kubectl get jobs -n "$NAMESPACE"
kubectl logs -n "$NAMESPACE" job/<job-name>
⚠ MKCOL works on GKE — but check where your seed job's writes land
Unlike Cloud Run, GKE's plain L4 LoadBalancer Service does not restrict
the WebDAV MKCOL method — confirmed live (201 Created). A real
CalDAV/CardDAV client can create new collections directly with no
workaround needed, which is one reason Radicale_GKE is the better fit for
heavier or production use.
However, the default seed-default-collections init job is a shared
Cloud-Run/GKE Common-module job and only mounts the shared GCS storage
bucket — it cannot attach to a StatefulSet's block PVC (a Kubernetes Job
can't mount a ReadWriteOnce PVC already held by a running Pod). So:
- With
stateful_pvc_enabled = true(the recommended production setting): the seed job's writes land in the otherwise-unused GCS bucket, and the "Default Calendar"/"Default Address Book" will not appear on the running pod's PVC-backed filesystem. This is harmless — create your first calendar via a real CalDAV client, orcurl -X MKCOL(confirmed working), instead of expecting the pre-seeded defaults. - Without a PVC (GCS-backed Deployment mode — not the recommended production configuration): the seed job's writes land in the same bucket the running pod mounts, so the defaults do appear.
4. Configuration Variables
Variables are grouped exactly as they appear on the deployment platform. Only settings specific to or notable for Radicale are listed; every other input is inherited from App_GKE with its standard behaviour.
Group 3 — Application Identity
| Variable | Default | Description |
|---|---|---|
application_name | radicale | Base name for resources. |
application_display_name | Radicale | Human-readable name shown in the platform UI. |
application_version | latest | Resolves to the pinned build RADICALE_VERSION=3.7.7 — GHCR tags have no v prefix. |
Group 4 — Runtime & Scaling
| Variable | Default | Description |
|---|---|---|
container_port | 5232 | Fixed via Radicale_Common; this variable is not forwarded to App_GKE. |
min_instance_count / max_instance_count | 0 / 1 | HPA scaling bounds; max is pinned to 1 non-negotiably. |
enable_image_mirroring | true | Mirrors the built image into Artifact Registry. |
Group 7 — StatefulSet
| Variable | Default | Description |
|---|---|---|
stateful_pvc_enabled | null | Recommended true for production — gives Radicale's collections filesystem real POSIX file locking. Auto-resolves workload_type to StatefulSet. |
stateful_pvc_mount_path | /var/lib/radicale | Must match the base image's own VOLUME declaration. |
stateful_pvc_storage_class | standard | HDD pd-standard, not SSD — collections are small text files with no high-IOPS need; avoids the tight SSD_TOTAL_GB quota. |
stateful_fs_group | 3000 | Makes the PVC group-writable; Radicale runs as UID 1000 / GID 2000. |
Group 14 — Cloud Storage & Artifact Registry
| Variable | Default | Description |
|---|---|---|
storage_buckets | one storage bucket | Mounted at /var/lib/radicale via GCS FUSE unless stateful_pvc_enabled = true, in which case the PVC takes over the same mount path. |
Group 16 — Database
| Variable | Default | Description |
|---|---|---|
database_type | NONE | Fixed by Radicale_Common — Radicale has no database of any kind. |
Group 11 — Workload Automation
| Variable | Default | Description |
|---|---|---|
initialization_jobs | seed-default-collections (injected by Radicale_Common) | See §3 for the GKE+PVC caveat. Providing a custom list replaces this default entirely. |
Group 10 — Observability & Health
| Variable | Default | Description |
|---|---|---|
startup_probe / liveness_probe | HTTP / | Radicale's unauthenticated 302 redirect to its web UI; both probe types treat 2xx–3xx as healthy. |
5. Outputs
| Output | Description |
|---|---|
service_name / service_url / service_external_ip | Kubernetes Service identity and address. |
storage_buckets | The storage bucket (unused as a mount when stateful_pvc_enabled = true). |
statefulset_name | Name of the StatefulSet, when workload_type = "StatefulSet". |
kubernetes_ready | Whether the workload reached Ready state. |
6. Configuration Pitfalls & Sensible Defaults
Risk: Critical (data loss / outage / security) — High (service degraded) — Medium (cost or partial degradation) — Low (minor).
| Setting | Sensible value | Risk | Consequence if wrong |
|---|---|---|---|
stateful_pvc_enabled | true for production | Medium | Without it, /var/lib/radicale is GCS FUSE-backed — acceptable given the single-instance cap, but not a real POSIX-locking filesystem. |
| Expecting default collections on a PVC-backed deployment | Create the first calendar via a real CalDAV client or curl -X MKCOL | Medium | The seed-default-collections job cannot mount a StatefulSet's ReadWriteOnce PVC, so its writes land in the unused GCS bucket instead — the pre-seeded defaults silently don't appear on the running pod's filesystem. |
max_instance_count | Leave at 1 | Critical | Radicale's storage backend is not designed for concurrent multi-instance access; raising this risks data corruption. |
stateful_pvc_storage_class | Leave at standard (HDD) | Low–Medium | Switching to standard-rwo/premium-rwo (SSD) draws from the far tighter SSD_TOTAL_GB quota for no real benefit — Radicale's I/O pattern doesn't need SSD IOPS. |
| Admin credential | Retrieve from Secret Manager after first deploy | Critical | Unlike apps with a well-known default login, Radicale generates a real secret — there is no way to log in until you retrieve ADMIN_PASSWORD. |
For the foundation behaviour referenced throughout — Workload Identity, ingress, autoscaling, CI/CD, Cloud Armor, IAP, Binary Authorization, VPC-SC, backups, and image mirroring — see App_GKE. Radicale-specific application configuration shared with the Cloud Run variant is described in Radicale_Common.