Docker services management

Scale and manage docker containers with services

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Docker services

Table of contents

  1. Initial assessments
  2. Swarm concepts
  3. Swarm management commands
  4. Services management commands

Initial assessments

  • This documentation is meant to be relevant primarily to the deployment of services in swarm mode by using docker stack deploy.
  • All the commands mentioned here are swarm compatible unless specified and must be run on the swarm manager (ie. the node managing the swarm).
  • Multiple services can be deployed on a swarm (whether using docker service or docker stack commands).

Swarm concepts

  • Docker swarm mode provides many additional capabilities for container-based applications :

    • Scaling
    • Networking
    • Securing
    • Maintaining

  • Swarms are not about dealing with individual containers :

    • Instead, all swarm workloads are scheduled as services (scalable groups of containers based on the same image).
    • Swarm mode adds and maintains service-wide networking features between containers.
    • Swarm objects can and should be described in manifests called stack files and based on the compose file specification.

  • When services running on a swarm need to be orchestrated (ie. a given service will start successfully only if some other services are available), 2 strategies exist :

    • Fine tune the restart policies of dependant service so that they initially fail, and then restart automatically once the services which are depended on are available.
    • Start the dependant services in replicated mode with zero replicas, and then run docker service scale to start the service containers once the services which are depended on are available.

Swarm management commands

  • Initialize / dismantle a swarm :
# initialize a docker swarm (the current node then become the swarm manager)
# optionally advertise the node interface, but this option is to be disregarded in most cases
docker swarm init --advertise-addr=eth0:2377

# make the current node join an existing swarm as a worker
# node must be capable to ping the swarm manager's ip address
docker swarm join --token "$token" "$ipaddress_manager:2377"

# make the current node (worker or manager) leave the swarm
# if the manager leaves the swarm, said swarm is gone
docker swarm leave --force
  • Manage swarm-specific overlay networks :
# create an overlay network on the current swarm for services to attach
# note : any compose application referencing this network will have to mention it as "external"
docker network create -o encrypted -d overlay "$network"

# remove overlay network from swarm (no running services must remain)
docker network rm "$network"

Services management commands

  • Setup / remove a service :
# deploy a new service $service based on $image on the current swarm
# scale to $replicas containers
# publish service port $container_port to node port $node_port
# attach service to overlay network $network
docker service create \
--name "$service" \
--replicas "$replicas" \
--publish "target=$node_port,published=$container_port" \
--network "$network" \
"$image"

# remove service $service from swarm
# (stops all containers, unpublishes ports, detach from network)
docker service rm "$service"
  • Setup / remove a stack :
# creates a new stack called $stack on current swarm using compose file $compose_file
docker stack deploy -c "$compose_file" "$stack"

# removes stack $stack from the swarm (stops all services and removes stack-specific overlay networks)
docker stack remove "$stack"
  • Retrieve informations on running services :
# list all services running on the current swarm
docker service ls

# list tasks (containers) for a specific service
docker service ps "$service"
  • Update a running service :
# scale service $service to $new_replicas containers
docker service scale "$service=$new_replicas"

# update service $service's base image to $new_image
# all containers will gradually restart with the new image
docker service update --image "$new_image" "$service" --force