Running Services in Docker 1.12
Great news! Docker for Windows and Mac is now in public beta, which means that Docker is that much easier to use for local development regardless of your preferred environment. You can download your preferred flavor of Docker at docker.com/getdocker.
Starting today, Docker for Mac and Windows also ships with Docker v1.12-rc2. With the new release, Docker becomes a really powerful tool for orchestrating your application.
What’s New in Docker 1.12?
Docker 1.12 comes with out-of-the-box capabilities for multi-container and multi-host app deployments, with networking and security built in. This means that with Docker 1.12 alone, you can deploy a highly available application to a Swarm cluster without needing to roll your own orchestration tools or spend a ton of hours trying to configure external orchestrators and network managers.
All of the orchestration features in 1.12 are backwards compatible. If you’re already an orchestration expert and have implemented your own solution, nothing will change. All of the extra orchestration features are opt-in.
To support the new orchestration capabilities, this release adds a couple new commands to the Docker API. Instead of only controlling things at a container level via
docker run my-image, you can now declare a desired state for a service using the command
docker service — provided you’ve set up your hosts in a Swarm cluster.
For example, I might want to run Elasticsearch as part of my application. With Docker 1.12 and using a Swarm cluster, I can scale out my Elasticsearch services quickly. Let’s start with just one replica of the Elasticsearch service:
~ $ docker service create --name elasticsearch elasticsearch 7u8dujdgrq8yk6tkqj6z8dcz8 ~ $ docker service ls ID NAME REPLICAS IMAGE COMMAND 7u8dujdgrq8y elasticsearch 0/1 elasticsearch
Take a peek at the service tasks to wait for the replica to fire up.
~ $ docker service tasks elasticsearch ID NAME SERVICE IMAGE LAST STATE DESIRED STATE NODE 4f8xsmbcfzukakyn9nfl1ojc2 elasticsearch.1 elasticsearch elasticsearch Running About a minute Running moby
We can see that one instance of the service is running now, and executing
docker service ls again will show that 1/1 replicas are up.
We can now take this service from 1 to 10 with just one command.
~ $ docker service update elasticsearch --replicas=10 elasticsearch ~ $ docker service ls ID NAME REPLICAS IMAGE COMMAND 7u8dujdgrq8y elasticsearch 10/10 elasticsearch
This feels a lot like
docker-compose scale, but it’s fully integrated as part of Docker Engine.
Monitor the individual tasks running against the service by executing
docker service tasks elasticsearch, and you’ll be able to see all 10 containers running. Note that
docker ps is specific to the host you’re on, so you may only see a small fraction of the total containers running. Don’t panic — that’s because they’re running on different hosts. Containers are implementation details with this new pattern. Rely on
docker service subcommands to check the state of your services.
All commands related to running services with the Docker API in 1.12 are declarative. This means that you tell Docker how you want your services to be running, and Docker takes over the work of making sure that the actual state of your cluster matches the declared state of your service. Instead of saying
docker run elasticsearch, which is an imperative statement just telling Docker to execute a command, the declarative
docker service create elasticsearch --name elasticsearch --replicas 10 elasticsearch is instructing Docker to make sure 10 instances of Elasticsearch are available at all times.
If a node in your cluster goes down or if a container fails, Docker takes care of restarting services to satisfy the declaration you made when you started the service. We can see this in action by simply nuking one of the Elasticsearch containers from orbit.
~ $ docker rm -f elasticsearch.6.54tytejr229scqfnwzrkbm7nt
If we’re super fast, we can catch our service in a state that doesn’t match our declared state of 10 replicas.
~ $ docker service ls ID NAME REPLICAS IMAGE COMMAND 7u8dujdgrq8y elasticsearch 9/10 elasticsearch
But give it a minute, and you’ll see that a new replica was created.
~ $ docker service ls ID NAME REPLICAS IMAGE COMMAND 7u8dujdgrq8y elasticsearch 10/10 elasticsearch
With v1.12, you have access to a powerful yet simple way create self-healing services running on a cluster of Swarm nodes, and this release helps make orchestration accessible for dev and ops alike.
There are tons of other cool features rolled into 1.12 related to networking and security. Check out the Docker blog post on 1.12. This new release is secure by default with end to end encryption, and also provides container-aware dynamic load balancing.
|Reference:||Running Services in Docker 1.12 from our WCG partner Laura Frank at the Codeship Blog blog.|