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.
What Radicale costs on RAD, and how that compares
Running Radicale in your own Google Cloud project costs about US$42.08/month in infrastructure, plus a one-time module fee of 75 RAD credits (sized at 1 vCPU / 1 GiB on GKE Autopilot pods). RAD charges the module fee once, at deploy time — never again on Update — plus build time metered in credits; Google Cloud usage itself is billed to your own billing account at Google's list price. On a RAD-managed project the same resources are metered hourly in credits at list price plus RAD's margin — about 67 credits/day — and the module fee is 10% lower, at 67.50 credits. See "Pause it for free" below for how a RAD-managed Radicale deployment can be stopped, at no running cost, until you need it again. (or see the Cloud Run guide for the lower-cost option)
What you pay on RAD
| Item | Own project | RAD-managed project |
|---|---|---|
| Module fee | 75 credits (once) | 67.50 credits (once) |
| Build time | ~3-6 credits, metered per build minute | same, metered in credits at list price + RAD's margin |
| Google Cloud running cost | ~$42.08/month, billed to your own billing account at Google's list price | ~67 credits/day, metered hourly at list price + RAD's margin |
Default running cost in your own project
| Resource | US$/month (Google list price, us-central1) |
|---|---|
| GKE Autopilot pod, 1x vCPU / 1 GiB | 36.08 |
| Cloud NAT and networking | 5 |
| Cloud Storage (add-ons, backups) | 1 |
| GKE cluster management fee* | shared across every GKE app in the project; $0 if this is your only cluster, else ~73 |
| Total | $42.08 |
* Not included in the total above — it is shared across every GKE app running in the same project, so it is $0 if this is your only GKE cluster.
How it compares
- We could not verify a current, directly-comparable commercial SaaS price for this exact open-source project, so the honest comparison is a bare self-managed server: Hetzner CPX22 (2 vCPU/4GB,
$24/mo), a DigitalOcean 2 vCPU/4GB Droplet ($24/mo), or a GCP Compute Engine e2-standard-2 (2 vCPU/8GB, ~$49/mo). This app's own footprint (1 vCPU or less, 1 GiB or less) is smaller than any of those classes, so a bare self-managed box sized to match would cost less than the figures above — but you would still own every patch, backup and security update yourself. - RAD is not claiming to beat a bare VPS on sticker price — it usually does not. What RAD adds for the same or a similar dollar figure is a managed database, Secret Manager-held credentials, monitoring, and one-click Update, none of which a bare VPS gives you for free.
- On a bare VPS you are the one applying OS/database security patches, taking and testing backups, and renewing certificates; RAD's managed Cloud SQL, Secret Manager and monitoring handle all three for you.
Pause it for free: delete a RAD-managed project, restore it when you need it
This is the headline option on a RAD-managed project, and it is free while paused. Deleting a RAD-managed project first unlinks its billing, then asks Google to delete the project itself — Google's own 30-day recoverable soft delete. Unlike deleting a single module, this does not tear down the database, any VM, or the compute resource one at a time: the whole project simply stops, and because billing is already unlinked, nothing is charged while it waits.
Restoring — within 30 days, and only by the project's owner — asks Google to undelete the project and reattaches its billing account, then asks you to run Update on each deployment to confirm everything came back. Because nothing was individually destroyed, that Update finds the same resources already there: it is a check, not a rebuild, and an Update never charges the module fee again. The whole restore costs only a handful of credits (under US$1) in build time for a typical chain of deployments. What this needs: you must own the project (not merely have RAD manage its billing), you must restore it yourself within the 30 days — after that Google deletes it for good — and restoring is admitted like creating a new project, so your purchased credit balance must still clear the tier's floor (100 credits for the sandbox tier most study and demo use fits). Google says most services are fully working again within 36 hours of a restore.
One real gap: nightly backups are written to a bucket inside the project, and that bucket has Cloud Storage's soft-delete explicitly turned off, so the backup bucket is very likely gone as soon as you delete the project — even though the project itself is recoverable for 30 days. If you have customised this deployment and want to keep that work, copy a backup out (to Google Drive, or a bucket outside the project) before deleting. For a default install with nothing irreplaceable in it, this does not matter.
Pay only while you use it, the other way: delete and redeploy
The other lever, for an own project (or a RAD-managed one past its 30-day restore window), is to delete Radicale outright and redeploy it later. A redeploy costs the module fee again plus the builds — roughly 78-81 credits in total for this module.
Deleting only saves money once Radicale would otherwise sit unused long enough to clear that redeploy cost against its own running cost — for this module, that is about 6 days or more of being idle, based on its own US$42.08/month running cost above. Most of that running cost is usually the database and any shared file/cache VM, and they stop only once nothing else in the project uses them, so deleting this app alone saves only its own compute share if something else shares the project.
Keep data first: nightly backups go to a bucket inside the deployment and are deleted with it, so copy the latest backup out before deleting if you want to keep it.
Lab sessions and Managed Environments
- Lab sessions, for training: a trainer runs a session for a class. Each participant gets the app in their own Google Cloud project for 15 minutes to 24 hours, within an allowance the trainer sets. Either the trainer funds every place, or each participant pays for their own. Everything is deleted when the session ends and unused credits go back to the trainer.
- Managed Environments, for consultancies: a partner runs the app for a client from a ring-fenced wallet it funds, and settles with the client directly. If the wallet runs low, billing pauses and the data is kept, so nobody receives an unexpected charge. At the end the partner hands the project over and the deployments become the client's own.
- Credits can be bought in more than 20 currencies, including XAF, XOF, NGN, GHS, KES and ZAR, by card, bank transfer or mobile money.
Sources (8 October 2026): Google Cloud Billing Catalog API list prices; radmodules.dev/pricing for RAD's own fees and daily-credit estimates; Resource Manager: delete and restore projects for the pause/restore mechanics.
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 | Block PVC by default (stateful_pvc_enabled = true); a storage GCS bucket is also provisioned and is the mount only if the PVC is turned off |
| 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 by default, and required.
stateful_pvc_enabled = true(auto-resolvesworkload_typetoStatefulSet) gives Radicale's collections filesystem real POSIX file locking and directory renames. On GCS FUSE, creating a calendar or address book fails, because gcsfuse cannot rename the temporary directory Radicale builds each collection in.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 = true(the default) the 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 default): 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): the seed job's writes land in the same bucket the running pod mounts, so the defaults do appear — but creating any further collection fails on GCS FUSE.
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 | true | Keep true — gives Radicale's collections filesystem real POSIX file locking and directory renames; on GCS FUSE, creating a collection fails. 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 (default) | High | Without it, /var/lib/radicale is GCS FUSE-backed, and creating a calendar or address book fails (gcsfuse cannot rename directories). |
| 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.
Related guides
- Hands-on lab: Radicale on GKE Autopilot — deploy it step by step, with the console screens and commands at each stage.
- Radicale on Google Cloud Run — the same application on Cloud Run, for when you need the other deployment target.
- Radicale Common — Shared Application Configuration — the configuration shared by both deployment targets.
Need RAD to do something it does not do yet? Request it on the roadmap, or vote on what is already there.