Gantry - Docker service updater

Gantry automatically updates selected docker swarm services to newer images with the same tag. It is inspired by but enhanced Shepherd.

Usage

Gantry is released as a container image. You can create a docker service and run it on a swarm manager node.

docker service create \
  --name gantry \
  --mode replicated-job \
  --constraint "node.role==manager" \
  --mount type=bind,source=/var/run/docker.sock,target=/var/run/docker.sock \
  shizunge/gantry

The examples folder contains example docker compose files, and more methods to launch Gantry, like at a specific time and via webhook.

You can also run Gantry as a script directly on the host outside the container

./src/entrypoint.sh

Gantry is written to work with busybox ash (v1.35+) as well as bash.

Configurations

You can configure the most behaviors of Gantry via environment variables.

Common

Environment Variable	Default	Description
GANTRY_LOG_LEVEL	INFO	Control how many logs generated by Gantry. Valid values are NONE, ERROR, WARN, INFO, DEBUG.
GANTRY_NODE_NAME		Add node name to logs. If not set, Gantry will use the host name of the Docker Swarm's manager, which is read from either the Docker daemon socket of current node or DOCKER_HOST.
GANTRY_POST_RUN_CMD		Command(s) to eval after each updating iteration. For example, you can use this to remove unused containers, networks and images and update standalone docker containers.
GANTRY_PRE_RUN_CMD		Command(s) to eval before each updating iteration. For example, you can use this to remove unused containers, networks and images and update standalone docker containers.
GANTRY_SLEEP_SECONDS	0	Interval between two updates. Set it to 0 to run Gantry once and then exit. When this is a non-zero value, after an updating, Gantry will sleep until the next scheduled update. The actual sleep time is this value minus time spent on updating services.
TZ		Set timezone for time in logs.

Gantry bases on Docker command line, environment variables for Docker command line also works for Gantry.

To login to registries

Environment Variable	Default	Description
GANTRY_REGISTRY_CONFIG		See Authentication.
GANTRY_REGISTRY_CONFIG_FILE		See Authentication.
GANTRY_REGISTRY_CONFIGS_FILE		See Authentication.
GANTRY_REGISTRY_HOST		See Authentication.
GANTRY_REGISTRY_HOST_FILE		See Authentication.
GANTRY_REGISTRY_PASSWORD		See Authentication.
GANTRY_REGISTRY_PASSWORD_FILE		See Authentication.
GANTRY_REGISTRY_USER		See Authentication.
GANTRY_REGISTRY_USER_FILE		See Authentication.

To select services

Environment Variable	Default	Description
GANTRY_SERVICES_EXCLUDED		A space separated list of services names that are excluded from updating.
GANTRY_SERVICES_EXCLUDED_FILTERS	label=gantry.services.excluded=true	A space separated list of filters, e.g. label=project=project-a. Exclude services which match the given filters from updating. The default value allows you to add label gantry.services.excluded=true to services to exclude them from updating. Note that multiple filters will be logical ANDED.
GANTRY_SERVICES_FILTERS		A space separated list of filters that are accepted by docker service ls --filter to select services to update, e.g. label=project=project-a. Note that multiple filters will be logical ANDED. Also see How to filters multiple services by name.

To check if new images are available

Environment Variable	Default	Description
GANTRY_MANIFEST_CMD	buildx	Valid values are buildx, manifest, and none. Set which command for manifest inspection. Also see FAQ section when to set GANTRY_MANIFEST_CMD. docker buildx imagetools inspect docker manifest inspect Set to none to skip checking the manifest. As a result of skipping, docker service update always runs. In case you add --force to GANTRY_UPDATE_OPTIONS, you also want to disable the inspection. You can apply a different value to a particular service via labels.
GANTRY_MANIFEST_NUM_WORKERS	1	The maximum number of GANTRY_MANIFEST_CMD that can run in parallel.
GANTRY_MANIFEST_OPTIONS		Options added to the docker buildx imagetools inspect or options to docker manifest inspect, depending on GANTRY_MANIFEST_CMD value, for all services. You can apply a different value to a particular service via labels.

To add options to services update

Environment Variable	Default	Description
GANTRY_ROLLBACK_ON_FAILURE	true	Set to true to enable rollback when updating fails. Set to false to disable the rollback. You can apply a different value to a particular service via labels.
GANTRY_ROLLBACK_OPTIONS		Options added to the docker service update --rollback command for all services. You can apply a different value to a particular service via labels.
GANTRY_UPDATE_JOBS	false	Set to true to update replicated-job or global-job. Set to false to disable updating jobs. Gantry adds additional options to docker service update when there is no running tasks. You can apply a different value to a particular service via labels.
GANTRY_UPDATE_NUM_WORKERS	1	The maximum number of updates that can run in parallel.
GANTRY_UPDATE_OPTIONS		Options added to the docker service update command for all services. You can apply a different value to a particular service via labels.
GANTRY_UPDATE_TIMEOUT_SECONDS	0	Error out if updating of a single service takes longer than the given time. Set to 0 to disable timeout. You can apply a different value to a particular service via labels.

After updating

Environment Variable	Default	Description
GANTRY_CLEANUP_IMAGES	true	Set to true to clean up the updated images on all hosts. Set to false to disable the cleanup. Before cleaning up, Gantry will try to remove any exited and dead containers that are using the images.
GANTRY_CLEANUP_IMAGES_OPTIONS		Options added to the docker service create command to create a global job for images removal. You can use this to add a label to the service or the containers.
GANTRY_NOTIFICATION_APPRISE_URL		Enable notifications on service update with Apprise. This must point to the notification endpoint (e.g. http://apprise:8000/notify)
GANTRY_NOTIFICATION_CONDITION	all	Valid values are all and on-change. Specifies the conditions under which notifications are sent. Set to all to send notifications every run. Set to on-change to send notifications only when there are updates or errors.
GANTRY_NOTIFICATION_TITLE		Add an additional message to the notification title.

Authentication

If you only need to login to a single registry, you can use the environment variables GANTRY_REGISTRY_USER, GANTRY_REGISTRY_PASSWORD, GANTRY_REGISTRY_HOST and GANTRY_REGISTRY_CONFIG to provide the authentication information. You may also use the *_FILE variants to pass the information through files. The files can be added to the service via docker secret. GANTRY_REGISTRY_HOST and GANTRY_REGISTRY_CONFIG are optional. Use GANTRY_REGISTRY_HOST when you are not using Docker Hub. Use GANTRY_REGISTRY_CONFIG when you want to enable authentication for only selected services.

If the images of services are hosted on multiple registries that are required authentication, you should provide a configuration file to the Gantry and set GANTRY_REGISTRY_CONFIGS_FILE correspondingly. You can use docker secret to provision the configuration file. The configuration file must be in the following format:

• Each line should contain 4 columns, which are either <TAB> or <SPACE> separated. The columns are

<configuration> <host> <user> <password>

• configuration: an identifier for the account. This is used as a path to Docker configuration files, which could be either a relative path or an absolute path.
• host: the registry to authenticate against, e.g. docker.io.
• user: the user name to authenticate as.
• password: the password to authenticate with.

• Lines starting with # are comments.
• Empty lines, comment lines and invalid lines are ignored.

You need to tell Gantry to use a named configuration rather than the default one when updating a particular service. The named configurations are set via either GANTRY_REGISTRY_CONFIG, GANTRY_REGISTRY_CONFIG_FILE or GANTRY_REGISTRY_CONFIGS_FILE. This can be done by adding the following label to the service gantry.auth.config=<configuration>. Gantry creates Docker configuration files and adds --config <configuration> to the Docker command line for the corresponding services.

NOTE: Gantry automatically adds --with-registry-auth to the docker service update command for a service, when it finds the label gantry.auth.config=<configuration> on the service, or when it logs in with the default Docker configuration. Without --with-registry-auth, the service will be updated to an image without digest. See this comment.

NOTE: You can use GANTRY_REGISTRY_CONFIGS_FILE together with other authentication environment variables.

NOTE: Gantry uses GANTRY_REGISTRY_PASSWORD and GANTRY_REGISTRY_USER to obtain Docker Hub rate when GANTRY_REGISTRY_HOST is empty or docker.io. You can also use their _FILE variants. If either password or user is empty, Gantry reads the Docker Hub rate for anonymous users.

Labels

Labels can be added to services to modify the behavior of Gantry for particular services. When Gantry sees the following labels on a service, it will modify the Docker command line only for that service. The value on the label overrides the global environment variables.

Label	Description
gantry.auth.config=<configuration>	See Authentication.
gantry.services.excluded=true	Exclude the services from updating if you are using the default GANTRY_SERVICES_EXCLUDED_FILTERS.
gantry.manifest.cmd=<command>	Override GANTRY_MANIFEST_CMD
gantry.manifest.options=<string>	Override GANTRY_MANIFEST_OPTIONS
gantry.rollback.on_failure=<boolean>	Override GANTRY_ROLLBACK_ON_FAILURE
gantry.rollback.options=<string>	Override GANTRY_ROLLBACK_OPTIONS
gantry.update.jobs=<boolean>	Override GANTRY_UPDATE_JOBS
gantry.update.options=<string>	Override GANTRY_UPDATE_OPTIONS
gantry.update.timeout_seconds=<number>	Override GANTRY_UPDATE_TIMEOUT_SECONDS

FAQ

FAQ

Migrate from Shepherd

Development

Gantry is written to work with busybox ash (v1.35+), thus it could run easily in an alpine-based container without additional packages installed. One exception is that the notification feature requires curl. Gantry is also tested in bash.

shellcheck will run on push to enforce the best practices of writing shell scripts. Some checks are disabled thanks to busybox ash supports more features than POSIX sh. You can find the list of disabled checks in .shellcheckrc.

To run shellcheck locally:

shellcheck src/*.sh tests/*.sh

The tests folder contains end-to-end tests, which cover the majority of the configuration options.

Contacts

If you have any problems or questions, please contact me through a GitHub issue.