Watchtower supports private Docker image registries. In many cases, accessing a private registry requires a valid username and password (i.e., _credentials_). In order to operate in such an environment, watchtower needs to know the credentials to access the registry.
The credentials can be provided to watchtower in a configuration file called `config.json`. There are two ways to generate this configuration file:
* The configuration file can be created manually.
* Call `docker login $REGISTRY_NAME` and share the resulting configuration file.
### Create the configuration file manually
Create a new configuration file with the following syntax and a base64 encoded username and password `auth` string:
```json
{
"auths": {
"$REGISTRY_NAME": {
"auth": "XXXXXXX"
}
}
}
```
`$REGISTRY_NAME` needs to be replaced by the name of your private registry (e.g., `my-private-registry.example.org`)
The required `auth` string can be generated as follows:
```bash
echo -n 'username:password' | base64
```
When the watchtower Docker container is stared, the created configuration file (`<PATH>/config.json` in this example) needs to be passed to the container:
```bash
docker run [...] -v <PATH>/config.json:/config.json containrrr/watchtower
```
### Share the Docker configuration file
To pull an image from a private registry, `docker login` needs to be called first, to get access to the registry. The provided credentials are stored in a configuration file called `<PATH_TO_HOME_DIR>/.docker/config.json`. This configuration file can be directly used by watchtower. In this case, the creation of an additional configuration file is not necessary.
When the Docker container is started, pass the configuration file to watchtower:
```bash
docker run [...] -v <PATH_TO_HOME_DIR>/.docker/config.json:/config.json containrrr/watchtower
```
When creating the watchtower container via docker-compose, use the following lines:
