An Introduction to Docker Swarm

What does docker swarm mean?

A Docker Swarm is an orchestration tool that runs Docker app. The swarm manager controls all the activities within the cluster, and machines in the cluster are called nodes.

What are the use cases for Docker Swarm?

Docker Swarm has a couple of worker nodes and minimum one manager node that is necessary for the efficient handling of the resources. For the Docker Swarm, there is no software-as-a-service, but it includes docker-ce

Key concepts of docker swarm

To understand Docker Swarm more, let’s discuss some of the main terms that are connected with Docker apps and containers.

If you are new to this topic, the basic term is Docker. This software platform is necessary for the containers’ integration into the development process. Such a platform is available for all users of Mac and Windows systems, and what is more beneficial, it has an open-source nature. This means a control interface is created between containerized apps and the host OS.

The major orientation of the Docker app is in terms of management and utilization. So that apps will be easily packed in containers with all the dependencies and code, and in such a way, they can function in any environment. Containerized apps can function smoothly when moving from one environment to another.

The next basic term is Image. It is a package of files that should be executed, and it includes all the libraries, code, binaries, and other necessities to run an app.

A Dockerfile is a file that defines the contents of the image. Let’s imagine that you want to write a program in Java. The machine that you are using doesn’t understand this code, so you need to somehow convert it into machine-understandable variant. This is called Java Runtime Environment and includes libraries, programs, and config files. In Docker, these assets relate to the Dockerfile.

There is no necessity in the installation of JRE on your machine, instead, you should download portable JRE and include it in the container. Once the app is launched from the container, all the resources will be in the containerized environment.

The major difference between Composer and Swarm is that Docker Compose configures several containers on the host, whereas Swarm connects containers to several hosts.   

Which two service types exist in Docker Swarm mode?

• Replicated. This type of service works depending on the number of replica tasks that are assigned to the available nodes.
• Global. This type of service works by scheduling one task to every node that is aligned with the specific requirements and constraints.

What roles do Docker Swarm nodes play?

Docker Swarm includes several virtual or physical machines that function in one cluster. Once machines become a part of the cluster, it is already a node. In the Docker Swarm, there are usually a couple of worker nodes and minimum one manager node that is dealing with the efficiency of resources. A load balancer functions on every node and deals with load requests across several hosts and containers.

Now, let’s review the major types of nodes:

Manager node in docker swarm

The major role of the manager node is to give tasks to the worker nodes. In addition to this, the manager node is dealing with some managerial tasks. The major recommendation regarding the number of these nodes is not to exceed seven manager nodes.

Leader node in docker swarm

After the establishment of the cluster, one of the available nodes is assigned as “leader”, this process is done with the help of the Raft consensus algorithm. This major node is responsible for the task orchestration as well as for management processes for the swarm.

In case the leader node is inaccessible because of some technical reasons, then another leader node can be chosen using the same algorithm.

Worker node in docker swarm

The worker nodes are getting and executing tasks that are assigned to them by the manager node. According to the default characteristics, all the manager nodes can also deal with the tasks of the working nodes in case they have enough resources.

Advantages of Docker Swarm: Is it right for you?

Harness container technology

One of the major advantage of the Docker Swarm is in its ability to fully utilize the container technology. Now, it is possible to deploy services or apps in a self-contained virtual environment, and before this technology, it was only possible to achieve it with a VM. Containers are lightweight, so it is possible to use computer power more efficiently.

Ensuring high availability with docker swarm

High availability of the app is now achievable because of the redundancy. There may be up to seven swarm managers that assign tasks. That means the availability of several managers can guarantee a better functioning even if one of the nodes stops working, because there are still some managers that continue to work.

Built-in load balancing

Tasks are scheduled with the usage of different methodologies. With the help of load balancing, it is possible to reach the maximum possible result when container workloads are assigned to the most optimal host.

Using complex strategy to monitor and analyze Docker containers

The issue with standard Linux-based tools is in their reliance on analyses of log files and some problems with scaling. Most companies search for a more centralized approach with container-aware tools for monitoring.

Start with the complex strategy to monitor Docker infrastructure. That involves lots of aspects, specifically configuration info, correlation of container events, and monitoring of daemon and host logs for a complete overview of the environment.