Preload Images

[skymichel]

Current Setup

WUD Version: 9.4.1
MQTT_HASS Integration: active

I'm triggering all updates manually through Home Assistant and therefore configured WUD_TRIGGER_DOCKERCOMPOSE_LOCAL_AUTO=false.
While reading the documentation I thought about combining _DRYRUN and _PRUNE in two separate triggers to automatically preload the new image version before the manually triggered update later that day.
I decided to add a WUD_TRIGGER_DOCKER_ with _AUTO=true (default) and _DRYRUN=true to preload the image as soon as the watcher finds a new version.
Unfortunately WUD chooses the update trigger by alphabetical order and therefore gives the WUD_TRIGGER_DOCKER_ precedence over WUD_TRIGGER_DOCKERCOMPOSE_ . This meant no update, but just repulling the new image.
Instead of using different trigger types I switched to the same type ( WUD_TRIGGER_DOCKER_ --> WUD_TRIGGER_DOCKERCOMPOSE_ ) and choose an appropriate name to match the alphabetical order.
This works quite nice with SemVer tags, but preloading floating tags results in watcher issues:

WARN
[watcher.docker.local]
Cannot get a reliable tag for this image [sha256:25a085eadc6c60d8fdf352158c45bdd85fbb86b7121319ac203cca1b9bb4f995]

Feature Request

Instead of manually excluding the Non-SemVer containers from DRYRUN-trigger and even having two triggers defined for the same scope, it would be nice to have new WUD_TRIGGER_DOCKER(COMPOSE)_{trigger_name}_PRELOAD parameter. The parameter should be evaluated as soon as _AUTO is set to false.
If _PRELOAD is set to false (default) everything works as of now.
If set to true, the new image should be pulled from registry, although _AUTO is set to false.
Non-SemVer/floating tags should be excluded from preloading to not accidentally update these containers during the next restart.

[fmartinou]

We investigated the mechanics behind this: pulling a floating tag (e.g. :latest) in Docker immediately repoints the local tag reference away from the running container to the new image ID. This strips RepoTags from the running container's image, which causes the Docker watcher to see an untagged image ID and log Cannot get a reliable tag for this image.

The solution we are adopting is adding a native WUD_TRIGGER_DOCKER(COMPOSE)_{name}_PRELOAD=true option (used when _AUTO=false on the same trigger, avoiding dual triggers and alphabetical precedence conflicts):

• For SemVer tags, it preloads the candidate tag directly.
• For floating tags, it preloads strictly by manifest digest (repo@sha256:<digest>). This pulls all layers into Docker's content-addressable cache without mutating the running container's tag pointer.

When you subsequently trigger the update manually, Docker finds all layers already cached locally, making the container recreation instantaneous. Implementation is underway!