What is Docker Swarm: Modes, Example and Working Updated

What is Docker Swarm: Modes, Example and Working Updated

What is Docker Swarm: Modes, Example and Working Updated

The final stage is to execute the tasks that have been assigned from the manager node to the worker node. In a docker swarm with numerous hosts, each worker node functions by receiving and executing the tasks that are allocated to it by manager nodes. By default, all manager modes are also worker nodes and are capable of executing tasks when they have the resources available to do so.

Worker nodes– receive and execute tasks dispatched from manager nodes. An agent runs on each worker node and reports on the tasks assigned to it to its manager node. When Docker is running in swarm mode, you can still run standalone containers on any of the Docker hosts participating in the swarm, as well as swarm services. A key difference between standalone containers and swarm services is that only swarm managers can manage a swarm, while standalone containers can be started on any daemon. Docker daemons can participate in a swarm as managers, workers, or both.

Advantages of Docker Swarm

The resulting image is a unit that’s easy to deploy and run as a container. Forfault tolerancein the Raft algorithm, you should always maintain an odd number 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. Raft requires a majority of manager nodes to agree on proposed updates to the swarm, such as node additions or removals.

docker swarm

The IP address must be assigned to a network interface available to the host operating system. All nodes in the swarm need to connect to the manager at the IP address. There are three types of docker swarm nodes which are given below. In this article, we not only installed Docker Engine, we also set up a Swarm Cluster, deployed a replicated service, and then created a Global Service. 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.


This gives much greater flexibility—but at the cost of having much more you need to know. Because of this, orchestration engines provide valuable services. These services compare favorably to what would be provided by the ideal operations team.

  • It is vital to realize that the scope of this license statement is only the Dockerfile and not the container image.
  • It is an alternative to other popular container orchestration tools, such as Kubernetes and Apache Mesos.
  • When we created the redis service, we specified that there should be 2 replicas.
  • Instead, all Swarm workloads are scheduled as services, which are scalable groups of containers with added networking features maintained automatically by Swarm.
  • To run Docker in swarm mode, you can either create a new swarm or have the container join an existing swarm.

The linux-image-extra package is a kernel specific package that's needed for Ubuntu systems to support the aufs storage driver. This driver is used by Docker for mounting volumes within containers. When we refresh Apt's package cache, Apt will look through all files within the sources.list.d/ directory to find new package repositories.

How to Configure a Docker Cluster Using Swarm

To strengthen our understanding of what Docker swarm is, let us look into the demo on the docker swarm. Before deploying a service in Swarm, the developer should implement at least a single node. Swarm node has a backup folder which we can use to restore the data onto a new Swarm. First, let’s dive into what Docker is before moving up to what docker swarm is. The service discovery makes no assumptions about your Swarm stack, in such a way that given proper configuration, this should be pluggable to any existing stack. Prometheus will only discover tasks and service that expose ports.

To run Docker in swarm mode, you can either create a new swarm or have the container join an existing swarm. The cluster management and orchestration features embedded in the Docker Engine are built using swarmkit. Swarmkit is a separate project which implements Docker’s orchestration layer and is used directly within Docker. We will assume that Prometheus runs on a Docker Swarm manager node and has access to the Docker socket at /var/run/docker.sock. The third one, services, will discover the services deployed in the swarm.

Install and set up

Running multiple manager nodes allows you to take advantage of swarm mode’s fault-tolerance features. However, adding more managers does not mean increased scalability or higher performance. Docker Swarm schedules tasks using a variety of methodologies to ensure that there are enough resources available for all of the containers. Through a process that can be described as automated load balancing, the swarm manager ensures that container workloads are assigned to run on the most appropriate host for optimal efficiency.

Accessing management functionality– swarm nodes can access the SwarmKit API and overlay networking, using an “advertise address” you specify for the manager node. If you don’t specify an address, and there is a single IP for the system, Docker listens by default on port 2377. SwarmKit is a toolkit for orchestrating distributed systems, including node discovery and task scheduling. There is a different join token for worker nodes and manager nodes. Manager tokens should be strongly protected, because any access to the manager token grants control over an entire swarm. To create a swarm– run thedocker swarm initcommand, which creates a single-node swarm on the current Docker engine.

docker swarm

We can once again check the status of this cluster by running the docker command. The service ps option will show the tasks for the specified service. In this example, https://globalcloudteam.com/ we can see the redis service has a task running on both of our swarm nodes. When creating the Swarm Cluster, we will need to designate a node manager.

Docker is a software platform that enables software developers to easily integrate the use of containers into the software development process. The Docker platform is open source and available for Windows and Mac, making it accessible for developers working on a variety of platforms. The application provides a control interface between the host operating system and containerized applications. These are services performed by using the swarm manager to schedule a single task to every available Node that meets the resource requirement and service constraints. It is a kind of software platform that enables the developers to integrate the use of containers seamlessly into software applications' development process.


As a result, centralized applications run seamlessly and reliably when they move from one computing environment to another. In a Docker application, a container is implemented by running an image. From this point on within this article, we will be executing tasks from several machines. To help make things a bit more clear, I have included the hostname in the command examples. The above apt-key command requests the specified key , from the p80.pool.sks-keyservers.net key server. This public key will be used to validate all packages downloaded from the new repository.

Seeinstallation instructions for all operating systems and platforms. Sumo Logic delivers a comprehensive strategy for continuous monitoring of Docker infrastructures. Correlate container events, configuration information, and host and daemon logs to get a complete overview of your Docker environment. Companies need a centralized approach to log management using container-aware monitoring tools. To contextualize our understanding of a Docker Swam, let's take a step back and define some of the more basic terms surrounding containers and the docker application.

However, it is easy to integrate load balancing through third-party tools in Kubernetes. The major difference between the platforms is based on complexity. On the other hand, Docker Swarm is designed for ease of use, making it a preferable choice for simple applications. Docker Swarm is quite simple to install, which is why it is well-suited for those just jumping into the container orchestration world. Today, Docker Swarm and Kubernetes are the most popular container orchestration platforms.

Swarm Mode Key Concepts

Let's take a look at what happens when we connect to swarm-03 over the redis published port. From the connection above, we were successful in connecting to the redis service. Since we have validated that the service is running, we can try to connect to this service from a remote system with the redis-cli client.

A container orchestration tool provides you with a framework to manage multiple containers. docker swarm icon builds on Docker and coordinates multiple instances of the Docker Engine. A swarm requires only a little more setup than installing Docker on more than one node. For these reasons, it doesn’t take much time or effort to get up and running with an orchestrator when using Docker in swarm mode. The Docker team has built it and consider it a “mode” of running Docker.

If no nodes have this amount of memory, the service will be pending until a node joins the swarm that satisfies the requirement. In addition to deploying to Swarm, we have also described our application as a stack file. This indicates 1/1 containers you asked for as part of your services are up and running. Also, we see that port 8000 on your development machine is getting forwarded to port 3000 in your getting-started container. Notice that in addition to your service, Swarm also creates a Docker network by default to isolate the containers deployed as part of your stack.

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