blumeops/docs/how-to/deployment/build-container-image.md

title	modified	last-reviewed	tags
Build Container Image	2026-04-11	2026-02-15	how-to containers ci

Build a Container Image

How to create a custom container image in BlumeOps, build it locally, and release it to the zot registry via the Forgejo CI pipeline.

Prerequisites

• Dagger CLI installed locally
• A container.py, Dockerfile, and/or default.nix for the service

1. Create the container directory

Add build files under containers/<name>/:

containers/<name>/
├── container.py    (native Dagger pipeline — preferred for new containers)
├── Dockerfile      (legacy — built via docker_build() fallback)
├── default.nix     (built by nix-build on the ringtail runner)
└── (optional scripts, configs)

A container can have one or more build files. The directory name becomes the image name: registry.ops.eblu.me/blumeops/<name>.

New containers for indri (k8s runner) should use container.py — native Dagger pipelines surface full build errors per step, while docker_build() (used for Dockerfiles) swallows errors. See containers/navidrome/container.py for the reference pattern. Existing Dockerfile containers are migrated incrementally during review-services.

Ringtail containers should continue using default.nix — these are built by nix-build on the ringtail runner and don't benefit from the Dagger migration.

2. Build locally

Any container (native container.py or legacy Dockerfile) — test with Dagger:

dagger call build --src=. --container-name=<name>

Nix — test with Dagger (no local nix required):

dagger call build-nix --src=. --container-name=<name> export --path=./<name>.tar.gz

Or with nix-build directly (requires nix, e.g. on ringtail):

nix-build containers/<name>/default.nix -o result

3. Release

Container builds are triggered manually. Shared Dagger helpers (src/blumeops/) affect all Dagger-built containers, making path-based auto-triggers unreliable.

To trigger a build:

mise run container-build-and-release <name>
mise run container-build-and-release <name> --ref <commit-sha>

Use --dry-run to preview without dispatching.

After dispatching, verify the workflow succeeded with runner-logs:

mise run runner-logs                    # find the new run number
mise run runner-logs <run#>             # see jobs and their status
mise run runner-logs <run#> -j <N>      # fetch full logs (e.g. on failure)

Build file	Workflow	Runner	Registry tag
container.py	build-container.yaml	k8s (indri)	:vX.Y.Z-<sha>
Dockerfile	build-container.yaml	k8s (indri)	:vX.Y.Z-<sha>
default.nix	build-container.yaml	nix-container-builder (ringtail)	:vX.Y.Z-<sha>-nix

The version (X.Y.Z) is extracted from VERSION in container.py (via dagger call container-version), ARG CONTAINER_APP_VERSION= in Dockerfiles, or version = "..." in default.nix. The SHA is the short (7-char) commit hash.

Check available images and tags with:

mise run container-list

4. Update k8s manifests

Change the image reference in argocd/manifests/<service>/deployment.yaml:

image: registry.ops.eblu.me/blumeops/<name>:vX.Y.Z-abc1234

Then deploy per deploy-k8s-service.

Squash-merge and container tags

Container image tags include the git commit SHA they were built from (e.g. v3.9.1-74029e1). When a PR is squash-merged, the original branch commits are replaced by a single new commit on main — the SHA in the image tag no longer exists on main. After branch cleanup (30 days), the SHA becomes unreachable and the container loses source traceability.

The rule: Production manifests must reference images built from a commit on main. After merging a PR that changed containers/<name>/:

1. Trigger a rebuild: mise run container-build-and-release <name>
2. Wait for the workflow to complete — verify with mise run runner-logs (find the run, check status)
3. Find the new main-SHA tag:

   mise run container-list <name>
   

   Tags marked [main] were built from a commit on main; tags marked [branch] are from PR branches
4. Commit a C0 follow-up updating the manifest to use the [main] tag:

   image: registry.ops.eblu.me/blumeops/<name>:vX.Y.Z-<main-sha>
   

This follow-up C0 is expected and routine — it's the cost of squash-merge + SHA-tagged containers.

Common Patterns

Existing containers demonstrate several build approaches:

Pattern	Example	Notes
Native Dagger (Go + Node)	#navidrome	container.py with helper functions — preferred for new containers
Alpine package install	#transmission	Simplest Dockerfile — install from apk
Go from source	#miniflux	Dockerfile: clone upstream, go build
Native Dagger (Elixir + Node)	#teslamate	container.py with Debian runtime — Elixir release with Node assets
Runtime tarball download	#kiwix-serve	Dockerfile: download pre-built binary with arch detection
Nix dockerTools	#ntfy-nix	buildLayeredImage with nix-built app (ringtail runner)

navidrome

containers/navidrome/container.py — Native Dagger build. Three-stage pipeline using helper functions: node_build() for UI, go_build() with CGO/taglib/FTS5 for backend, alpine_runtime() with ffmpeg. This is the reference pattern for migrating Dockerfile containers to native Dagger builds.

transmission

containers/transmission/Dockerfile — Installs transmission-daemon directly from Alpine packages. Good starting point for services available in apk. (Legacy Dockerfile — migrate to container.py during review.)

miniflux

containers/miniflux/Dockerfile — Two-stage Go build. Clones upstream at a pinned version tag, runs make, copies the binary into a minimal Alpine runtime. (Legacy Dockerfile — migrate to container.py during review.)

teslamate

containers/teslamate/container.py — Native Dagger build. Two-stage pipeline: Elixir builder with Node.js for asset compilation, Debian slim runtime. Uses Debian-based images (not Alpine) due to Elixir/OTP dependencies. Includes entrypoint script for pg-wait and migrations.

kiwix-serve

containers/kiwix-serve/Dockerfile — Downloads a pre-built binary from upstream, with architecture detection for cross-platform support. (Legacy Dockerfile — migrate to container.py during review.)

ntfy (nix)

containers/ntfy/default.nix — Builds ntfy from source using buildGoModule and packages it with dockerTools.buildLayeredImage. Runs alongside the existing Dockerfile; the nix variant is tagged :version-nix in the registry. Nix containers should continue using default.nix.

Related

• deploy-k8s-service — Deploying the service that uses the image
• create-release-artifact-workflow — Alternative: release non-container artifacts
• dagger — Dagger CI reference