Introduction to Docker Swarm Mode

A service is a description of a task, whereas a task performs the work. Services can be used and accessed by any node of the same cluster. Services can be deployed in two different ways – global and replicated. Before the inception of Docker, developers predominantly relied on virtual machines. But unfortunately, virtual machines lost their popularity as it was proven to be less efficient.

  • You can use Compose to run multiple containers that are connected over a number of user defined networks, but this solution is always limited to a single host.
  • We will do this by adding an entry within the /etc/apt/sources.list.d/ directory.
  • The status of the current node in your swarm can be verified using the node ls command.
  • For example, the desired state might be running three instances of an HTTP listener, with load balancing between them.

Beginning with Docker Engine 1.9, Docker container networks require specific Linux kernel versions. Higher kernel versions are usually preferred, but carry an increased risk of instability because of the newness of the kernel. Where possible, use a kernel version that is already approved for use in your production environment. If you can not use a 3.10 or higher Linux kernel version for production, you should begin the process of approving a newer kernel as early as possible. For example, many companies not only deploy dedicated isolated infrastructures for production – such as networks, storage, compute and other systems. They also deploy separate management systems and policies.


Removing a stack is similar to removing a service and can be done using the rm command. You can check the limitations of your service using the inspect command. The –secret tag can be used to add a secret while creating a service. Getting the logs of a service is very similar to getting the logs of a single container.

docker swarm example

As you can see, the service logs are displayed for all tasks that belong to the service. We stay on the local machine for this exercise, I hope your computer has the power to run two virtual machines in parallel. If you don’t have the power, you can do this exercise on Play with Docker. Once you have defined all the variables, deploy to your cluster using the following freestyle step. You can runswarm join-token –rotateat any time to invalidate the older token and generate a new one, for security purposes. Docker will shortly supportKubernetes Guideas well as Docker Swarm, and Docker users will be able to use either Kubernetes or Swarm to orchestrate their container workloads.

Step 2: Uninstall Old Versions of Docker

This is the magic of Docker swarm’s routing mesh mechanism, which provides intrinsic feature of load balance and failover. You should give careful consideration to the operating system that your Swarm infrastructure relies on. While such architectures may appear to provide the ultimate in availability, there are several factors to consider. Consul, etcd, and Zookeeper are all suitable for production, and should be configured for high availability. You should use each service’s existing tools and best practices to configure these for HA.

docker swarm example

Having an odd number of managers results in a higher chance that a quorum remains available to process requests, if the network is partitioned into two sets. A single manager node can be created but the worker node can not be created without a manager node. The ideal number for the count of the manager node is seven. Increasing the number of the manager node does not mean that the scalability will increase. The swarm manager will then migrate any containers running on the drained node elsewhere in the cluster.

The Application

We used the docker service scale command before to scale our service. If you want to change the set-up, you have to change the service configuration. If you need to run a command in a running container with exec, then you need to work with the container directly. The deploy option, for example is only supported by Swarm. You can use the deploy setting to describe your deployment configuration in a Swarm.

docker swarm example

For this reason, a container network requires a key-value store to maintain network configuration and state. This KV store can be shared in common with the one used by the Swarm cluster discovery service. However, for best performance and fault isolation, you should deploy individual KV store instances for container networks and Swarm discovery. This is especially so in demanding business critical production environments. If you’re familiar with Docker Compose, defining stacks is very similar to the definition of a multi-service composed application on a single Docker host.

Security Containers: System Call and Permissions

It allows the creation of a swarm of docker nodes that can deploy application services. As the first party solution, no additional software is needed to use Swarm orchestration to create and manage a cluster. Services running on the same stack have an overlay network that lets them communicate with each other. Instead of hard coding IP addresses in your code, you can simply use the name of the service as the hostname you want to connect to. And because this works seamlessly in development with docker-compose and in production with Docker Swarm, it’s one less thing to worry about when deploying your app. A service is a description of a task or the state, whereas the actual task is the work that needs to be done.

Tutorial: Deploy a Full-Stack Application to a Docker Swarm – The New Stack

Tutorial: Deploy a Full-Stack Application to a Docker Swarm.

Posted: Mon, 12 Sep 2022 07:00:00 GMT [source]

The following sections discuss some technologies and best practices that can help you build high performance Swarm clusters. It is possible to share the same Consul, etcd, or Zookeeper containers between the Swarm discovery and Engine container networks. However, for best performance and availability you should deploy dedicated instances – a discovery instance for Swarm and another for your container networks. The following sections discuss some technologies and best practices that can enable you to build resilient, highly-available Swarm clusters. You can then use these cluster to run your most demanding production applications and workloads.

Creating a Swarm:

The service Address 1 is the IP address for the load balancer. You can test the connectivity using wget within the busybox. You can see all currently deployed services with the command below. If you run into problems joining nodes to the swarm, you can have the problematic node leave the cluster with the command below. Once the update is completed, reboot the nodes to start using the new version. Once all settings are ready, start the node by clicking the Deploy server button at the bottom of the page.

You may want to drain a node in your Swarm to conduct maintenance activities. When you drain a node, Docker will make sure that the node will not receive new tasks and the existing tasks will be rescheduled to active nodes. We have 6 replicas of our Node application running and one replica of visualizer. Please be patient, it takes some time to apply all the changes. Many options are similar to the options of docker container run and you’ll find options that are specific to Swarm mode. You can remove your stack with the docker stack rm command.

Add deployment configuration to the Compose file

Let’s not use it right now, we’ll still need our running stack. The task is a scheduling slot for your containers in the service. The notion of service in the Swarm follows the same concept.

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