With watchtower you can update the running version of your containerized app simply by pushing a new image to the Docker Hub or your own image registry. Watchtower will pull down your new image, gracefully shut down your existing container and restart it with the same options that were used when it was deployed initially. Run the watchtower container with the following command:
- [Usage](#usage)
- [Arguments](#arguments)
- [Available Options](#available-options)
* [Help](#help)
* [Cleanup](#cleanup)
* [Debug](#debug)
* [Docker host](#docker-host)
* [Include stopped](#include-stopped)
* [Poll Interval](#poll-interval)
* [Filter by enable label](#filter-by-enable-label)
* [Notifications via E-Mail](#notifications-via-e-mail)
* [Notifications through Slack webhook](#notifications-through-slack-webhook)
* [Notifications via MSTeams incoming webhook](#notifications-via-msteams-incoming-webhook)
- [Contributors](#contributors)
## Overview
Watchtower is an application that will monitor your running Docker containers and watch for changes to the images that those containers were originally started from. If watchtower detects that an image has changed, it will automatically restart the container using the new image.
With watchtower you can update the running version of your containerized app simply by pushing a new image to the Docker Hub or your own image registry. Watchtower will pull down your new image, gracefully shut down your existing container and restart it with the same options that were used when it was deployed initially.
For example, let's say you were running watchtower along with an instance of _centurylink/wetty-cli_ image:
```bash
$ docker ps
CONTAINER ID IMAGE STATUS PORTS NAMES
967848166a45 centurylink/wetty-cli Up 10 minutes 0.0.0.0:8080->3000/tcp wetty
6cc4d2a9d1a5 containrrr/watchtower Up 15 minutes watchtower
```
Every few minutes watchtower will pull the latest _centurylink/wetty-cli_ image and compare it to the one that was used to run the "wetty" container. If it sees that the image has changed it will stop/remove the "wetty" container and then restart it using the new image and the same `docker run` options that were used to start the container initially (in this case, that would include the `-p 8080:3000` port mapping).
## Usage
Watchtower is itself packaged as a Docker container so installation is as simple as pulling the `containrrr/watchtower` image. If you are using ARM based architecture, pull the appropriate `containrrr/watchtower:armhf-<tag>` image from the [containrrr Docker Hub](https://hub.docker.com/r/containrrr/watchtower/tags/).
Since the watchtower code needs to interact with the Docker API in order to monitor the running containers, you need to mount _/var/run/docker.sock_ into the container with the -v flag when you run it.
Run the `watchtower` container with the following command:
```bash
docker run -d \
--name watchtower \
-v /var/run/docker.sock:/var/run/docker.sock \
containrrr/watchtower
```
If pulling images from private Docker registries, supply registry authentication credentials with the environment variables `REPO_USER` and `REPO_PASS`
or by mounting the host's docker config file into the container (at the root of the container filesystem `/`).
Passing environment variables:
```bash
docker run -d \
--name watchtower \
-e REPO_USER=username \
-e REPO_PASS=password \
-v /var/run/docker.sock:/var/run/docker.sock \
containrrr/watchtower container_to_watch --debug
```
Also check out [this Stack Overflow answer](https://stackoverflow.com/a/30494145/7872793) for more options on how to pass environment variables.
If you mount the config file as described above, be sure to also prepend the url for the registry when starting up your watched image (you can omit the https://). Here is a complete docker-compose.yml file that starts up a docker container from a private repo at dockerhub and monitors it with watchtower. Note the command argument changing the interval to 30s rather than the default 5 minutes.
```json
version: "3"
services:
cavo:
image: index.docker.io/<org>/<image>:<tag>
ports:
- "443:3443"
- "80:3080"
watchtower:
image: containrrr/watchtower
volumes:
- /var/run/docker.sock:/var/run/docker.sock
- /root/.docker/config.json:/config.json
command: --interval 30
```
## Arguments
By default, watchtower will monitor all containers running within the Docker daemon to which it is pointed (in most cases this will be the local Docker daemon, but you can override it with the `--host` option described in the next section). However, you can restrict watchtower to monitoring a subset of the running containers by specifying the container names as arguments when launching watchtower.
```bash
docker run -d \
--name watchtower \
-v /var/run/docker.sock:/var/run/docker.sock \
containrrr/watchtower nginx redis
```
In the example above, watchtower will only monitor the containers named "nginx" and "redis" for updates -- all of the other running containers will be ignored.
If you do not want watchtower to run as a daemon you can pass a run-once flag and remove the watchtower container after it's execution.
```bash
docker run --rm \
-v /var/run/docker.sock:/var/run/docker.sock \
containrrr/watchtower --run-once nginx redis
```
In the example above, watchtower will execute an upgrade attempt on the containers named "nginx" and "redis". Using this mode will enable debugging output showing all actions performed as usage is intended for interactive users. Once the attempt is completed, the container will exit and remove itself due to the "--rm" flag.
When no arguments are specified, watchtower will monitor all running containers.
## Available options
Any of the options described below can be passed to the watchtower process by setting them after the image name in the `docker run` string, for example:
```bash
docker run --rm containrrr/watchtower --help
```
### Help
Shows documentation about the supported flags.
```
Argument: --help
Environment Variable: N/A
Type: N/A
Default: N/A
```
### Cleanup
Removes old images after updating. When this flag is specified, watchtower will remove the old image after restarting a container with a new image. Use this option to prevent the accumulation of orphaned images on your system as containers are updated.
```
Argument: --cleanup
Environment Variable: WATCHTOWER_CLEANUP
Type: Boolean
Default: false
```
### Debug
Enable debug mode with verbose logging.
```
Argument: --debug
Environment Variable: N/A
Type: Boolean
Default: false
```
### Docker host
Docker daemon socket to connect to. Can be pointed at a remote Docker host by specifying a TCP endpoint as "tcp://hostname:port".
```
Argument: --host, -h
Environment Variable: DOCKER_HOST
Type: String
Default: "unix:///var/run/docker.sock"
```
### Include stopped
Will also include created and exited containers.
```
Argument: --include-stopped
Environment Variable: WATCHTOWER_INCLUDE_STOPPED
Type: Boolean
Default: false
```
### Poll Interval
Poll interval (in seconds). This value controls how frequently watchtower will poll for new images.
```
Argument: ---interval, -i
Environment Variable: WATCHTOWER_POLL_INTERVAL
Type: Integer
Default: 300
```
### Filter by enable label
Watch containers where the `com.centurylinklabs.watchtower.enable` label is set to true.
```
Argument: --label-enable
Environment Variable: WATCHTOWER_LABEL_ENABLE
Type: Boolean
Default: false
```
### Without updating containers
Will only monitor for new images, not update the containers.
```
Argument: --monitor-only
Environment Variable: WATCHTOWER_MONITOR_ONLY
Type: Boolean
Default: false
```
### Without pulling new images
Do not pull new images. When this flag is specified, watchtower will not attempt to pull
new images from the registry. Instead it will only monitor the local image cache for changes.
Use this option if you are building new images directly on the Docker host without pushing
them to a registry.
```
Argument: --no-pull
Environment Variable: WATCHTOWER_NO_PULL
Type: Boolean
Default: false
```
### Run once
Run an update attempt against a container name list one time immediately and exit.
```
Argument: --run-once
Environment Variable: WATCHTOWER_RUN_ONCE
Type: Boolean
Default: false
```
### Scheduling
[Cron expression](https://godoc.org/github.com/robfig/cron#hdr-CRON_Expression_Format) in 6 fields (rather than the traditional 5) which defines when and how often to check for new images. Either `--interval` or the schedule expression could be defined, but not both. An example: `--schedule "0 0 4 * * *"`
```
Argument: --schedule, -s
Environment Variable: WATCHTOWER_SCHEDULE
Type: String
Default: -
```
### Wait until timeout
Timeout before the container is forcefully stopped. When set, this option will change the default (`10s`) wait time to the given value. An example: `--stop-timeout 30s` will set the timeout to 30 seconds.
```
Argument: --stop-timeout
Environment Variable: WATCHTOWER_TIMEOUT
Type: Duration
Default: 10s
```
### TLS Verification
Use TLS when connecting to the Docker socket and verify the server's certificate. See below for options used to configure notifications.
```
Argument: --tlsverify
Environment Variable: DOCKER_TLS_VERIFY
Type: Boolean
Default: false
```
## Linked Containers
Watchtower will detect if there are links between any of the running containers and ensure that things are stopped/started in a way that won't break any of the links. If an update is detected for one of the dependencies in a group of linked containers, watchtower will stop and start all of the containers in the correct order so that the application comes back up correctly.
For example, imagine you were running a _mysql_ container and a _wordpress_ container which had been linked to the _mysql_ container. If watchtower were to detect that the _mysql_ container required an update, it would first shut down the linked _wordpress_ container followed by the _mysql_ container. When restarting the containers it would handle _mysql_ first and then _wordpress_ to ensure that the link continued to work.
## Stopping Containers
When watchtower detects that a running container needs to be updated it will stop the container by sending it a SIGTERM signal.
If your container should be shutdown with a different signal you can communicate this to watchtower by setting a label named _com.centurylinklabs.watchtower.stop-signal_ with the value of the desired signal.
This label can be coded directly into your image by using the `LABEL` instruction in your Dockerfile:
Or, it can be specified as part of the `docker run` command line:
```bash
docker run -d --label=com.centurylinklabs.watchtower.enable=false someimage
```
If you need to only include only some containers, pass the --label-enable flag on startup and set the _com.centurylinklabs.watchtower.enable_ label with a value of true for the containers you want to watch.
Or, it can be specified as part of the `docker run` command line:
```bash
docker run -d --label=com.centurylinklabs.watchtower.enable=true someimage
```
## Remote Hosts
By default, watchtower is set-up to monitor the local Docker daemon (the same daemon running the watchtower container itself). However, it is possible to configure watchtower to monitor a remote Docker endpoint. When starting the watchtower container you can specify a remote Docker endpoint with either the `--host` flag or the `DOCKER_HOST` environment variable:
Note in both of the examples above that it is unnecessary to mount the _/var/run/docker.sock_ into the watchtower container.
### Secure Connections
Watchtower is also capable of connecting to Docker endpoints which are protected by SSL/TLS. If you've used _docker-machine_ to provision your remote Docker host, you simply need to volume mount the certificates generated by _docker-machine_ into the watchtower container and optionally specify `--tlsverify` flag.
The _docker-machine_ certificates for a particular host can be located by executing the `docker-machine env` command for the desired host (note the values for the `DOCKER_HOST` and `DOCKER_CERT_PATH` environment variables that are returned from this command). The directory containing the certificates for the remote host needs to be mounted into the watchtower container at _/etc/ssl/docker_.
With the certificates mounted into the watchtower container you need to specify the `--tlsverify` flag to enable verification of the certificate:
```bash
docker run -d \
--name watchtower \
-e DOCKER_HOST=$DOCKER_HOST \
-e DOCKER_CERT_PATH=/etc/ssl/docker \
-v $DOCKER_CERT_PATH:/etc/ssl/docker \
containrrr/watchtower --tlsverify
```
## Updating Watchtower
If watchtower is monitoring the same Docker daemon under which the watchtower container itself is running (i.e. if you volume-mounted _/var/run/docker.sock_ into the watchtower container) then it has the ability to update itself. If a new version of the _containrrr/watchtower_ image is pushed to the Docker Hub, your watchtower will pull down the new image and restart itself automatically.
## Notifications
Watchtower can send notifications when containers are updated. Notifications are sent via hooks in the logging system, [logrus](http://github.com/sirupsen/logrus).
The types of notifications to send are passed via the comma-separated option `--notifications` (or corresponding environment variable `WATCHTOWER_NOTIFICATIONS`), which has the following valid values:
- `email` to send notifications via e-mail
- `slack` to send notifications through a Slack webhook
- `msteams` to send notifications via MSTeams webhook
### Settings
- `--notifications-level` (env. `WATCHTOWER_NOTIFICATIONS_LEVEL`): Controls the log level which is used for the notifications. If omitted, the default log level is `info`. Possible values are: `panic`, `fatal`, `error`, `warn`, `info` or `debug`.
### Notifications via E-Mail
To receive notifications by email, the following command-line options, or their corresponding environment variables, can be set:
- `--notification-email-from` (env. `WATCHTOWER_NOTIFICATION_EMAIL_FROM`): The e-mail address from which notifications will be sent.
- `--notification-email-to` (env. `WATCHTOWER_NOTIFICATION_EMAIL_TO`): The e-mail address to which notifications will be sent.
- `--notification-email-server` (env. `WATCHTOWER_NOTIFICATION_EMAIL_SERVER`): The SMTP server to send e-mails through.
- `--notification-email-server-tls-skip-verify` (env. `WATCHTOWER_NOTIFICATION_EMAIL_SERVER_TLS_SKIP_VERIFY`): Do not verify the TLS certificate of the mail server. This should be used only for testing.
- `--notification-email-server-port` (env. `WATCHTOWER_NOTIFICATION_EMAIL_SERVER_PORT`): The port used to connect to the SMTP server to send e-mails through. Defaults to `25`.
- `--notification-email-server-user` (env. `WATCHTOWER_NOTIFICATION_EMAIL_SERVER_USER`): The username to authenticate with the SMTP server with.
- `--notification-email-server-password` (env. `WATCHTOWER_NOTIFICATION_EMAIL_SERVER_PASSWORD`): The password to authenticate with the SMTP server with.
The full documentation is available at https://containrrr.github.io/watchtower.
To receive notifications in Slack, add `slack` to the `--notifications` option or the `WATCHTOWER_NOTIFICATIONS` environment variable.
Additionally, you should set the Slack webhook url using the `--notification-slack-hook-url` option or the `WATCHTOWER_NOTIFICATION_SLACK_HOOK_URL` environment variable.
By default, watchtower will send messages under the name `watchtower`, you can customize this string through the `--notification-slack-identifier` option or the `WATCHTOWER_NOTIFICATION_SLACK_IDENTIFIER` environment variable.
Other, optional, variables include:
- `--notification-slack-channel` (env. `WATCHTOWER_NOTIFICATION_SLACK_CHANNEL`): A string which overrides the webhook's default channel. Example: #my-custom-channel.
- `--notification-slack-icon-emoji` (env. `WATCHTOWER_NOTIFICATION_SLACK_ICON_EMOJI`): An [emoji code](https://www.webpagefx.com/tools/emoji-cheat-sheet/) string to use in place of the default icon.
- `--notification-slack-icon-url` (env. `WATCHTOWER_NOTIFICATION_SLACK_ICON_URL`): An icon image URL string to use in place of the default icon.
To receive notifications in MSTeams channel, add `msteams` to the `--notifications` option or the `WATCHTOWER_NOTIFICATIONS` environment variable.
Additionally, you should set the MSTeams webhook url using the `--notification-msteams-hook` option or the `WATCHTOWER_NOTIFICATION_MSTEAMS_HOOK_URL` environment variable.
MSTeams notifier could send keys/values filled by `log.WithField` or `log.WithFields` as MSTeams message facts. To enable this feature add `--notification-msteams-data` flag or set `WATCHTOWER_NOTIFICATION_MSTEAMS_USE_LOG_DATA=true` environment variable.
Simon Aronsson
6 years ago