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Radicale on Google Cloud Run

Radicale on Google Cloud Run

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 Cloud Run v2 on top of the App_CloudRun foundation, which provisions and manages the shared Google Cloud 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 Cloud Run application — service identity, ingress and load balancing, scaling and concurrency, CI/CD, Cloud Armor, IAP, Binary Authorization, VPC Service Controls, backups, and the deployment lifecycle — refer to the App_CloudRun 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$17.58/month in infrastructure, plus a one-time module fee of 40 RAD credits (sized at 1 vCPU / 1 GiB on a scale-to-zero Cloud Run instance). 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 3 credits/day — and the module fee is 10% lower, at 36 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 GKE guide if you need Kubernetes)

What you pay on RAD​

ItemOwn projectRAD-managed project
Module fee40 credits (once)36 credits (once)
Build time~3-6 credits, metered per build minutesame, metered in credits at list price + RAD's margin
Google Cloud running cost~$17.58/month, billed to your own billing account at Google's list price~3 credits/day, metered hourly at list price + RAD's margin

Default running cost in your own project

ResourceUS$/month (Google list price, us-central1)
Cloud Run, 1x vCPU / 1 GiB (scaleToZero)11.58
Cloud NAT and networking5
Cloud Storage (add-ons, backups)1
Total$17.58

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 43-46 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 8 days or more of being idle, based on its own US$17.58/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 container on Cloud Run v2. The deployment wires together a small, focused set of Google Cloud services:

CapabilityGoogle Cloud serviceNotes
ComputeCloud Run v2Single Python process, 1 vCPU / 1 GiB by default, scale-to-zero
DatabasenoneRadicale stores every collection as plain files — no Cloud SQL instance is created
Object storageCloud StorageA storage bucket is mounted at /var/lib/radicale via GCS FUSE — the single source of truth for all data
Cache & queuenoneRadicale has no Redis or queue dependency
SecretsSecret ManagerA real generated ADMIN_PASSWORD — Radicale ships with no default admin account at all
IngressCloud Run URLDefault run.app URL; optional external HTTPS load balancer + custom domain

Sensible defaults worth knowing up front:

  • No database of any kind. Radicale_Common fixes database_type = "NONE" — Radicale is a pure filesystem store.
  • Custom, thin-wrapper build. Radicale_Common layers a cloud entrypoint onto the official ghcr.io/kozea/radicale image via Cloud Build, then mirrors the result into Artifact Registry.
  • No default admin account — a real generated secret. Unlike apps that ship a well-known first-login credential, Radicale's auth defaults to denyall until configured. Radicale_Common generates and injects a real ADMIN_PASSWORD on every deployment (see the Common guide).
  • max_instance_count pinned to 1, min_instance_count defaults to 0. 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 is blocked at the edge on Cloud Run — read §3 before you deploy. Creating a new calendar/address book normally requires the WebDAV MKCOL method, which Google's Cloud Run frontend rejects before it ever reaches the container. A default seed job works around this — see below.

2. Google Cloud Services & How to Explore Them​

All commands assume PROJECT and REGION are set. Service and resource names are reported in the deployment Outputs.

A. Cloud Run — the Radicale service​

  • Console: Cloud Run → select the service for revisions, traffic, logs, and metrics.
  • CLI: 
    gcloud run services list --project "$PROJECT" --region "$REGION"
    gcloud run services describe <service-name> --project "$PROJECT" --region "$REGION"

See App_CloudRun for scaling, concurrency, and traffic splitting.

B. Cloud Storage — the single source of truth​

The storage bucket is mounted at /var/lib/radicale via GCS FUSE. Every calendar, address book, item, and the generated htpasswd/config files live here — losing this bucket loses all Radicale state.

  • CLI: 
    gcloud storage buckets list --project "$PROJECT" --filter="name~radicale"
    gcloud storage ls "gs://<bucket-name>/collections/collection-root/"

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: 
    gcloud run services describe <service-name> --region "$REGION" --format='value(status.url)'

E. Cloud Logging & Monitoring​

  • CLI: 
    gcloud run services logs read <service-name> --project "$PROJECT" --region "$REGION" --limit 50

3. Radicale Application Behaviour​

  • No first-deploy database setup. There is no db-init job — Radicale has no database to bootstrap.
  • seed-default-collections runs 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, bypassing HTTP entirely. This exists because of a genuine platform limitation — see the callout below.
  • No default admin account. Radicale's auth defaults to denyall until an htpasswd file exists. Radicale_Common generates a real ADMIN_PASSWORD and the cloud entrypoint writes both the INI config and a bcrypt htpasswd entry on every boot (not just first boot — there's no user table to check "already initialized" against).
  • Health path. Startup and liveness probes target / — Radicale's unauthenticated 302 redirect to its web UI, treated as healthy by both probe types.
  • Inspect job execution: 
    gcloud run jobs executions list --job <job-name> --project "$PROJECT" --region "$REGION"

⚠ MKCOL is blocked by Cloud Run's frontend — the most important thing to know about this module​

Creating a new collection (calendar or address book) via the standard CalDAV/CardDAV protocol requires the WebDAV MKCOL HTTP method. Confirmed live through extensive debugging across three separate deployment attempts:

  • Google's Cloud Run frontend (GFE) rejects MKCOL at the edge with a generic "400 Bad Request" Google error page — the request never reaches the Radicale container. Every other method (GET, PUT, PROPFIND) passes through fine; this is specific to MKCOL.
  • Cloud Run services have no shell/exec access, so there is no manual operator workaround after the fact either.
  • Without a fix, a fresh Radicale_CloudRun deployment would be unable to create any calendar — not through a standard client (Apple Calendar, Thunderbird, DAVx5), and not even through Radicale's own web UI, which also issues MKCOL internally.

The fix: Radicale_Common's default seed-default-collections init job writes the collection directory structure directly onto the storage volume — a plain container with filesystem access, no HTTP/GFE layer involved. This runs automatically on every deploy (execute_on_apply = true) and seeds a "Default Calendar" and "Default Address Book" for the admin user. Verified live: a PROPFIND on the admin's principal correctly lists both collections, and a real VEVENT can be PUT and GET successfully.

If you need additional collections beyond the two seeded defaults, you cannot create them via a standard client on Cloud Run. Either supply a custom initialization_jobs entry that writes them the same way, or use Radicale_GKE, whose plain L4 LoadBalancer Service has no MKCOL restriction.

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_CloudRun with its standard behaviour.

Group 3 — Application Identity​

VariableDefaultDescription
application_nameradicaleBase name for resources.
application_display_nameRadicaleHuman-readable name shown in the platform UI and Cloud Run console.
application_versionlatestResolves to the pinned build RADICALE_VERSION=3.7.7 — GHCR tags have no v prefix.

Group 4 — Runtime & Scaling​

VariableDefaultDescription
container_port5232Radicale's native default port.
min_instance_count / max_instance_count0 / 1Scale-to-zero; max is pinned to 1 non-negotiably.
enable_image_mirroringtrueMirrors the built image into Artifact Registry (avoids GHCR rate limits).
container_protocolhttp1Correct — Radicale serves plain HTTP/1.1.

Group 11 — Storage & Filesystem​

VariableDefaultDescription
storage_bucketsone storage bucketMounted at /var/lib/radicale via GCS FUSE — the single source of truth for all Radicale state.
gcs_volumes[]The storage bucket mount is added automatically; use this for additional volumes only.

Group 12 — Database Backend​

VariableDefaultDescription
database_typeNONEFixed by Radicale_Common — Radicale has no database of any kind.

Group 13 — Jobs & Scheduled Tasks​

VariableDefaultDescription
initialization_jobsseed-default-collections (injected by Radicale_Common)Works around the Cloud Run MKCOL restriction — see §3. Providing a custom list replaces this default entirely.

Group 14 — Observability & Health​

VariableDefaultDescription
startup_probe / liveness_probeHTTP /Radicale's unauthenticated 302 redirect to its web UI; both probe types treat 2xx–3xx as healthy.

5. Outputs​

OutputDescription
service_name / radicale_urlCloud Run service name and internal/public URL (note: this output is named radicale_url, not service_url).
storage_bucketsThe storage bucket backing /var/lib/radicale.
deployment_id / tenant_id / resource_prefixNaming identifiers.
project_id / project_numberProject identifiers.
initialization_jobsCreated initialization job names (includes seed-default-collections).

6. Configuration Pitfalls & Sensible Defaults​

Risk: Critical (data loss / outage / security) — High (service degraded) — Medium (cost or partial degradation) — Low (minor).

SettingSensible valueRiskConsequence if wrong
Creating new collections via a CalDAV/CardDAV clientRely on the seeded defaults, or use Radicale_GKE for arbitrary new collectionsHighMKCOL is rejected at the Cloud Run edge (GFE) before reaching the container — no standard client, and not even Radicale's own web UI, can create a NEW collection on this platform. Only the two collections seeded at deploy time exist unless you supply a custom init job.
max_instance_countLeave at 1CriticalRadicale's storage backend uses OS-level file locking and is not designed for concurrent multi-instance access; raising this risks data corruption.
Admin credentialRetrieve from Secret Manager after first deployCriticalUnlike apps with a well-known default login, Radicale generates a real secret — there is no way to log in until you retrieve ADMIN_PASSWORD.
stateful_pvc_enabled (n/a on Cloud Run)Use Radicale_GKE for productionMediumCloud Run's GCS FUSE mount has weaker file-locking semantics than Radicale's storage backend expects; acceptable only because concurrency is capped at 1 instance.

For the foundation behaviour referenced throughout — service identity, scaling and concurrency, ingress and load balancing, CI/CD, Cloud Armor, IAP, Binary Authorization, VPC-SC, backups, and image mirroring — see App_CloudRun. Radicale-specific application configuration shared with the GKE variant is described in Radicale_Common.

Need RAD to do something it does not do yet? Request it on the roadmap, or vote on what is already there.

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