Docker Swarm: An Introduction

Docker swarm is orchestrator for docker containers.

1. It can be used to deploy docker containers in a cluster.
2. The cluster has one or more managers and multiple workers.
3. The docker engine on the cluster nodes have the docker swarm mode (as of docker 1.12 release) which can be used to register nodes to the swarm cluster (no separate service registry is required). It internally uses Consul for service registration. No separate swarm agent container is required to run on each cluster node anymore like it was required before 1.12 release.
4. The same docker compose file can be used to deploy application locally on one host and in swarm cluster. So no separate deployment files for development and production modes. This is an advantage compared to kubernetes where we have docker-compose file for development on a single host only and kubernetes specific deployment file for deployment in kubernetes cluster in production.
5. Once a cluster is provisioned, docker swarm will manage on which node the service container gets deployed.
6. Docker swarm will also ensure that at any time the number of container replicas remains same. So if a node goes down or a container crashes, it will start new container for the application service such that the total number of replicas remain same as configured initially. This is same as what Amazon Auto scaling group (ASG) does.