Software development

Docker Swarm definition & overview

In contrast, Kubernetes is complex but powerful and provides self-healing, auto-scaling capabilities out of the box. K3s, a lightweight form of Kubernetes certified by CNCF, can be the right choice if you want the benefits of Kubernetes without all of the learning overhead. Hence, while you might have downtime on Docker Compose, Docker Swarm ensures that your app keeps running with the help of backup servers .

To add another node worker, we can simply repeat the installation and setup steps in the first part of this article. Since we already covered those steps, we’ll skip ahead to the point where we have a three-node Swarm Cluster. We can once again check the status of this cluster by running the docker command.


The user can deploy manager and worker nodes at runtime in the Docker engine’s swarm mode. Docker Swarm is another open-sourcecontainer orchestrationplatform that has been around for a while. Swarm — or more accurately,swarm mode — is Docker’s native support for orchestrating clusters ofDockerengines. A Swarm cluster consists of Docker Engine-deployed Swarm manager nodes and worker nodes . Container orchestration refers to the automation of management and operational logistics behind containerized workloads.

what is docker swarm

The manager node then uses the scheduler to assign and reassign tasks to nodes as required and specified in the Docker service. Another reason to use Docker Swarm is that multiple hosts run tasks concurrently in a cluster. This is in contrast to Docker Compose, which only allows you to run multiple containers on one Docker engine. So the manager node actively monitors the state of each worker node and activates a fail-tolerant mechanism to reschedule the task from a failed node to another.

About Docker Swarm Rocks

Because all of the containers share the services of a single operating system kernel, they use fewer resources than virtual machines. Today, containerization has transformed how we deploy software and work with microservices. As the trend of working with Linux-based virtual containers for developing applications continues to evolve, it has brought in higher demands for their management and deployment. So far, we have discussed the pros and cons of each platform in general. We will compare the two platforms in terms of their setup requirements, app deployment capabilities, availability and scaling, monitoring features, security, and load balancing. Nodes are individual instances of the Docker engine that control your cluster and manage the containers used to run your services and tasks.

  • A given Docker host can be a manager, a worker, or perform both roles.
  • This section compares the features of Docker Swarm and Kubernetes and the weaknesses/strengths of choosing one platform over the other.
  • Swarm is also easier to pick up, even with less technical knowledge.
  • At this point, both of these nodes should have Docker Engine installed based on the instructions above.
  • A service is a description of a task, whereas a task performs the work.

This enables the application to run in a variety of locations, such as on-premises, in public or private cloud. Docker on macOS uses a Linux virtual machine to run the containers. A single machine can serve as both a manager and worker node, in which case workloads can run on any server in the swarm. Their power lies in easy scaling, environment-agnostic portability, and flexible growth.

Kubernetes vs. Docker Swarm – A comparison

We can see that when the service was created as a Global Service, a task was then started on every node worker within our Swarm Cluster. With the service now created, we can see how Docker distributed our tasks for this service by once again executing the docker command with the service ps options. When Docker publishes a port for a service, it does so by listening on that port across all nodes within the Swarm Cluster.

what is docker swarm

Load balancing is also a part of Docker Swarm clusters and it is used to route requests across nodes. If somehow the leader node becomes unavailable due to some fatal error or hardware failure, another node is against chosen from the available nodes. The Node which is chosen as the leader has the responsibility to make all of the swarm management, also make the decisions for the swarm. In this write-up, we learned what is Docker Swarm, along with that understood the Swarm mode key concepts and how Docker Swarm works.

It provides automated load balancing within the Docker containers, whereas other container orchestration tools require manual efforts. An IT administrator controls Swarm through a swarm manager, which orchestrates and schedules containers. The swarm manager allows a user to create a primary managerinstanceand multiple replica instances in case the primary instance fails. In Docker Engine’s swarm mode, the user can deploy manager and worker nodes at runtime. Developers love using docker swarm because it fully leverages the design advantages offered by containers.

Docker Inc. was founded by Kamel Founadi, Solomon Hykes, and Sebastien Pahl during the Y Combinator Summer 2010 startup incubator group and launched in 2011. The startup was also one of the 12 startups in Founder’s Den first cohort. Hykes started the Docker project in France as an internal project within dotCloud, a platform-as-a-service company.

Updating a deployed service

Replicated services are instantiated as many times as you’ve requested. Global services, on the other hand, are like Kubernetes DaemonSets, in that you have one instance running on each node. Enterprise Swarm is now offered as an alternative orchestration type with Mirantis Kubernetes Engine . Users can access the Mirantis Kubernetes Engine webUI to switch nodes to Swarm or ‘mixed’ (i.e., Kubernetes+Swarm) mode at will. Open source Docker Engines can also be combined in a swarm, using CLI commands. Docker Swarm provides high availability as you can easily duplicate the microservices in Docker Swarm.

what is docker swarm

Despite the fact that Kubernetes is a tried-and-true all-in-one framework with a vast set of APIs and consistent cluster states, its complexity slows down the deployment of new containers. To establish clusters in Docker Swarm, you only need to know a few commands. Furthermore, the configuration is the same across operating systems, making it easy for developers to get started regardless of whatever OS they’re using. The Worker node establishes a connection with the Manager node and monitors for new tasks.

What is Docker and Docker Container?

So you can always revert new swarm configurations to the state of a former one. Say the manager node on a previous swarm fails; you can start a new cluster with more manager nodes and revert it to adapt the configuration of the previous one. Forfault tolerancein the Raft algorithm, you should always maintain an odd number magento cloud docker of managers in the swarm to better support manager node failures. 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. Other nodes can access the SwarmKit API using the manager node’s advertised IP address.

Disadvantages of Docker Swarm

Each Docker host in this cluster is a node, also called a worker node. Raft requires a majority of manager nodes to agree on proposed updates to the swarm, such as node additions or removals. ALeadervalue identifies the primary manager node that makes all swarm management and orchestration decisions for the swarm. A docker swarm usually contains specific numbers of nodes and also has one manager node at least.

It’s something that either remote systems or other containers within the swarm can connect to and consume. Because both Kubernetes and Docker Swarm are container orchestration tools, they have many of the same features. However, each tends to shine in different aspects, which can mean one or the other might be the best fit depending on your needs and preferences. The Google-created Kubernetes and Docker’s own Docker Swarm are the two powerhouse tools for container orchestration.

Now, let us try to understand docker swarm with the help of an example. Say we have one manager node and three worker nodes inside the swarm cluster and two simple dockerised applications which need deployment . In such cases, we will simply launch A1 and A2 as services with the required number of replicas onto the swarm. Docker Swarm is smart enough to properly load balance all the tasks in the most efficient way onto the worker nodes. Now say, W3 node becomes unhealthy, then the tasks running on it will be redistributed to the remaining healthy worker nodes.

Any kernel updates to this system should include the installation of the appropriate linux-image-extra package version that coincides with the new kernel version. If this package is not updated as well, some issues may arise with Docker’s ability to mount volumes. Before installing Docker Engine, we need to install a prerequisite package.

Docker can use different interfaces to access virtualization features of the Linux kernel. That doesn’t however, mean there’s a clear answer as to which is “better”. There are many factors that determine which is better for you, such as existing environment, target environment, application complexity, and so on.

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