mkfares · August 13, 2020 14:43 · Aug 13, 2020
diff --git a/docker-swarm-services.md b/docker-swarm-services.md
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+# Docker Swarm - Managing Services
+Services are configurations of tasks that are intended to be run on swarm nodes. Usually, services belong to a stack which is defined in a docker compose file. However, services can be created and managed using the command line interface.
+
+## List services in a swarm
+The ls commands lists all running services in a swarm. 
+
+```
+$ docker service ls
+```
+
+## Inspect a service
+The inspect command displays detailed information about a service. The output is displayed in JSON format.
+```
+$ docker service inspect [options] <service-name>
+$ docker service inspect vote_vote
+```
+Options:  
+-f : Formats the output using the given Go template  
+--pretty : Prints the information in a human friendly format
+
+To display the service information in pretty format (Indented format):
+```
+$ docker service inspect --pretty vote_vote
+```
+
+Use the -f option to display a specific information about a service. 
+```
+$ docker service inspect -f '{{.Endpoint.Ports}}' vote_vote
+```
+## Show logs of a service
+The logs command fetches the logs of a service or a task. The logs are messages send by the service/task to the standard output and standard error streams. The service logs include all logs of the service tasks.
+
+```
+$ docker service logs [options] <service-name> | <task_id>
+$ docker service logs vote_db
+$ docker service logs 332dm0jcsssg
+```
+Options:  
+--follow : Continues streaming the new output from the service’s stdout and stderr streams.  
+--details: Shows more log details  
+--tail : Shows a specific number of lines from the end of the logs  
+--since: Shows the service logs generated after a given date.
+
+## List tasks of a service
+The ps command lists the tasks, or replicas, that belong to a service.
+
+```
+$ docker service ps [options] <service-name>
+$ docker service ps vote_redis
+```
+
+When a service is part of a stack, the service name has the format: \<stack-name>_\<service-name-in-compose-file>
+
+## Create a service
+A service can be created using the command line interface instead of using a docker compose file. The command "service create" creates a new service based on the provided options. 
+
+```
+$ docker service create [options] <image-name> [command][arguments]
+```
+
+The create command has multiple options that are equivalent to the options in the docker compose file.
+
+Before creating a service, you may clean your swarm from all stacks by removing them using the "stack rm" command.
+```
+$ docker stack rm $(docker stack ls --format '{{.Name}}')
+$ docker stack ls
+```
+
+The option --name set a name to the new service. The option -p publishes a port to the outside of the swarm.
+```
+$ docker service create --name web -p 8080:80 nginx:stable
+$ docker service ls
+```
+
+Options:  
+-d : Returns the prompt to user immediately  
+--entrypoint: Overwrites the entrypoint option of an image  
+-e : Sets environment variables for replicas  
+--limit-cpu : Limits the number of cpu dedicated to the service   
+--limit-memory : Limits the memory size dedicated to the service  
+--mode : Can be either replicated or global (one replica per node)  
+--network : Attaches the service to a network    
+--mount : Attaches a filesystem to a service  
+-p : Publishes a port  
+--replicas : Sets the number of replicas  
+--restart-condition : Restarts when condition is met (none | on-failure | any ) (default “any”)  
+--delay-update : Sets the delay between updates  
+--update-parallelism : Sets the number of tasks updated simultaneously   
+
+## Update a service
+The docker swarms allows a rolling update of services. A rolling update is an update of a certain number of replicas of a service at the same time. This avoids downtime and makes the service available during service update.  
+
+```
+$ docker service update [options] <service-name>
+```
+
+The options of the "service create" command can be used with the "service update" command.
+
+```
+$ docker service create --name web --replicas 5 -p 8080:80 nginx:latest
+$ docker service update --publish-add 8181:80 web
+```
+
+The number of tasks, or replicas, to be updated at the same time is specified using the --update-parallelism option.
+
+```
+$ docker service update --update-parallelism 2 --image nginx:stable web
+```
+
+A time delay between updates of the service replicas can be set as follows:
+```
+$ docker service update --update-parallelism 2 --update-delay 5s --image nginx:mainline web
+```
+
+When an error occur during the update, a rollback to previous version of the service configuration can be performed.
+
+```
+$ docker service rollback <service-name>
+$ docker service rollback web
+```
+
+## Scale a service
+The scale command permits the increase or the decrease of the number of replicas of a service. The scaling of services may take some time to complete. 
+```
+$ docker service scale <service-name>=<number-of-replicas> [options]
+$ docker service scale vote_vote=3
+```
+To verify the number of replicas for the vote_vote service:
+```
+$ docker service ls
+```
+
+The REPLICAS column shows both the actual and desired number of tasks for the service.
+
+The option -d returns the prompt to the user instead of waiting for the verification of scale to be stable.
+```
+$ docker service scale vote_vote=5 -d
+```
+
+## Remove a service
+The rm command removes a service from a swarm. The command does not ask for confirmation to remove a service. 
+
+```
+docker service rm <service-name>
+docker service rm web
+```
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