What is the significance of the --with-registry-auth flag when deploying a service in Docker Swarm?

What is the significance of the --with-registry-auth flag when deploying a service in Docker Swarm?

The --with-registry-auth flag in the context of Docker Swarm is used when deploying a service, and it is typically associated with private container registries that require authentication. Here's an explanation:

The --with-registry-auth flag is used during the deployment of a service in Docker Swarm to ensure that the worker nodes have the necessary authentication credentials to access private container registries. When deploying a service that uses images from a private registry, this flag ensures that the Docker daemon on each worker node is provided with the authentication credentials required to pull the private images during service creation.

For example, when deploying a service with an image hosted on a private registry, the deployment command might look like this:

docker service create --with-registry-auth --replicas 3 myservice:latest

In this command:

  • --with-registry-auth: This flag instructs Docker Swarm to use the authentication credentials of the local Docker daemon when pulling images from private registries. It passes the credentials stored on the manager node to the worker nodes.

Without this flag, worker nodes might not have the necessary credentials to pull images from private registries, leading to authentication errors during service deployment. Including --with-registry-auth ensures a seamless deployment process when private registry authentication is required.