Learn Docker Swarm Mode - scale in 5 minutes!

Wow, sitting in the second row of the Dockercon Keynote today - there is so much new stuff in Docker 1.12! As a member of the Docker for Mac Beta program I got early access to Docker 1.12RC and pulled it down and updated my machine last night while waiting for Dockercon to start in Seattle. It was a 100MB update and my hotel WiFi is really fast (said nobody ever).

After updating I was still able to point at Docker 1.11 servers and run my previous workloads with the legacy Swarm version. YMMV, but do try the update.

I wanted to look at the new docker service command. I'd seen a sneak preview of this from Mike Goelzer and tried to re-create from memory what he'd shown me about a week earlier.

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

Usage:    docker service COMMAND

Manage Docker services

Options:  
      --help   Print usage

Commands:  
  create      Create a new service
  inspect     Inspect a service
  tasks       List the tasks of a service
  ls          List services
  rm          Remove a service
  scale       Scale one or multiple services
  update      Update a service

Run 'docker service COMMAND --help' for more information on a 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 (216.58.193.110): 56 data bytes  
64 bytes from 216.58.193.110: seq=0 ttl=37 time=0.527 ms  
64 bytes from 216.58.193.110: seq=1 ttl=37 time=0.629 ms  

Here's the equivalent command with docker service create:

$ docker service create --name ping1 busybox ping docker.com
1hakvrpkl01zque7u17dxox41  

I've assigned a name to the service so that we can reference it easily, but Docker has also generated a GUID of 1hakvrpkl01zque7u17dxox41.

docker service ls

To check which services we have running/created type in docker service ls as below:

$ docker service ls
ID            NAME            REPLICAS  IMAGE    COMMAND  
1hakvrpkl01z  ping1           1/1       busybox  ping docker.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 ping1=5
ping1 scaled to 5  

We will now see that the docker service ls command gives 5/5 replicas as running and docker ps will show 5 unique containers running, too.

$ docker service ls
ID            NAME            REPLICAS  IMAGE    COMMAND  
1hakvrpkl01z  ping1           5/5       busybox  ping docker.com  
docker scale rm

Once you have finished your work either scale back to 0 or remove the service with docker service rm ping1

And so much more

Head over to part 2 now where we will scale up a microservice across the new Swarm Mode. Check out more of the exciting new features over on the Docker blog now.

Part 2: scale a real GUID-generating microservice

See also:

My Dockercon 2016 Speaker notes, recap + IoT Swarm demo

Alex Ellis

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United Kingdom http://alexellis.io/