To deploy an application image when Docker Engine is in swarm mode, you create a service. Frequently a service will be the image for a microservice within the context of some larger application. Examples of services might include an HTTP server, a database, or any other type of executable program that you wish to run in a distributed environment. For more: Docker
When you create a service, you specify which container image to use and which commands to execute inside running containers. You also define options for the service including:
- the port where the swarm will make the service available outside the swarm
- an overlay network for the service to connect to other services in the swarm
- CPU and memory limits and reservations
- a rolling update policy
- the number of replicas of the image to run in the swarm
Starting with a service
Let’s pick a service or a long running container. This could be the sleep 500 command, but we can just as easily make it ping docker.com.
Have a look at the new docker service command’s help page:
# docker service
Let’s go one by one docker service command.
docker service create
docker service create is synonymous with docker run, so anything we can do with docker run should work the same.
# docker run busybox ping google.com PING google.com (172.217.6.78): 56 data bytes 64 bytes from 172.217.6.78: seq=0 ttl=46 time=76.507 ms 64 bytes from 172.217.6.78: seq=1 ttl=46 time=76.387 ms 64 bytes from 172.217.6.78: seq=2 ttl=46 time=76.376 ms 64 bytes from 172.217.6.78: seq=3 ttl=46 time=76.325 ms
Here’s the equivalent command with docker service create:
# docker service create --name ping busybox ping foxutech.com
3uyw3cqsdwizqenk7jcgv1sbq
We have create the service with name, which we can refer it easily in future for our reference. This help us to refresh anytime our service and also its generated GUID of assigned a name to the service so that we can reference it easily, but Docker has also generated a GUID of 3uyw3cqsdwizqenk7jcgv1sbq.
docker service ls
Check which services we have running/created type in docker service ls as below:
# docker service ls ID           NAME REPLICAS IMAGE   COMMAND 3uyw3cqsdwiz ping 1/1      busybox ping foxutech.com
docker service scale
Scaling this has never been easier, we just type in the name of the service and how many replicas we want.
# docker service scale ping=4
this command make ping service scaled to 4
We will now see that the docker service ls command gives 4/4 replicas as running and docker ps will show 4 unique containers running, too.
# docker service ls ID                    NAME REPLICAS IMAGE    COMMAND 3uyw3cqsdwiz ping 4/4      busybox ping foxutech.com
docker scale remove
Once you have finished your work either scale back to 0 or remove the service with docker service rm ping
# docker service rm ping
Update a Service
You can change almost everything about an existing service using the docker service update command. When you update a service, Docker stops its containers and restarts them with the new configuration.
Since Nginx is a web service, it will work much better if you publish port 80 to clients outside the swarm. You can specify this when you create the service, using the -p or –publish flag. When updating an existing service, the flag is –publish-add. There is also a –publish-rm flag to remove a port that was previously published.
Assuming that the webserver service from the previous section still exists, use the following command to update it to publish port 80.
# docker service update --publish-add 80 webserver
To verify that it worked, use docker service ls:
# docker service ls ID           NAME      REPLICAS IMAGE               COMMAND 0nbjrzb080mf webserver 1/1      motoskia/apache-php # docker ps
Remove a Service
To remove a service, use the docker service remove command. You can remove a service by its ID or name, as shown in the output of the docker service ls command. The following command removes the ping service.
# docker service remove ping
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