====== Docker Swarm ======
  * Deploy stack from compose file
<code>
docker stack deploy --compose-file docker-compose.yml stackdemo
</code>
  * Delete stack
<code>
docker stack rm stackdemo
</code>
  * Add a secret
<code>
echo "This is an external secret" | docker secret create my_external_secret -
# or
docker secret create my_external_secret secret_file_path
</code>
  * Remove a secret
<code>
docker secret rm my_external_secret
</code>
  * Use a secret in compose file
<code>
version: '3.7'

services:
  web:
    image: nginxdemos/hello
    secrets:                    # secrets block only for 'web' service
     - my_external_secret
     - my_file_secret

secrets:                        # top level secrets block
  my_external_secret:
    external: true
  my_file_secret:
    file: my_file_secret.txt
</code>
  * Update a service
<code>
docker service update --image DOCKER_IMG SERVICE_NAME
</code>