What is the use of docker cluster?

The role of the docker cluster: abstract several Docker hosts into a whole, and uniformly manage various Docker resources on these Docker hosts through an entrance (cluster manager). The advantages of docker clusters include: scalable expansion, rolling upgrade, fast deployment and online deployment, etc.

The operating environment of this tutorial: linux5.9.8 system, docker-1.13.1 version, Dell G3 computer.

What is the use of docker cluster?

A cluster is a group of multiple machines running docker and added to a group. After joining the cluster, you can continue to run your own docker commands, but now these machines are managed by the cluster manager in the cluster. executed on.

To put it simply, it abstracts several Docker hosts into a whole, and manages various Docker resources on these Docker hosts through one entrance (cluster manager).

For large companies, docker clusters have great advantages, including scalable expansion, rolling upgrades, and fast deployment and online deployment.

Docker container can package your program in the Linux system, and then isolate your program from other programs. It is equivalent to installing a software on a virtual machine, which has nothing to do with the software on the computer. Contact, but the biggest difference between it and a virtual machine is that its performance overhead is particularly small.

The machines in the cluster can be physical or virtual. After joining the group, each machine is called a node. The cluster manager can use different strategies to manage running containers, such as: emptyest node, which is used to fill the least utilized containers; global to ensure that each machine can only get one instance of the specified container service.

You can write these policies into files to execute the cluster manager's policies.

The cluster manager is the only machine in the cluster that can execute commands. You can also authorize other machines to join the cluster management work. Authorized machines can only do what Workers are just there to provide capacity and cannot tell other machines what to do or what not to do.

After docker turns on the cluster mode, your machine becomes a cluster manager, and then the commands run by docker will be commands to manage the cluster, not just run on your current machine.

docker cluster manager-Swarm

Docker Swarm includes two aspects: an enterprise-level Docker security cluster, and a microservice application orchestration engine.

In terms of clustering, Swarm organizes one or more Docker nodes so that users can manage them in a cluster.

Swarm has built-in encrypted distributed cluster store, encrypted network, public TLS (Mutual TLS), secure cluster access token (Secure Cluster Join Token) and a A set of PKI (Public Key Infrastructure) that simplifies digital certificate management. We can add or delete nodes freely.

In terms of orchestration, Swarm provides a rich set of APIs that make it easy to deploy and manage complex microservice applications. By defining your application in a declarative configuration file, you can deploy it using native Docker commands.

In addition, you can even perform rolling upgrades, rollbacks, and expansion and contraction operations, which can also be completed based on simple commands.

In the past, Docker Swarm was an independent product based on the Docker engine. Since Docker version 1.12, it has been fully integrated into the Docker engine and can be enabled by executing a single command. By 2018, it will be able to deploy and manage Kubernetes applications in addition to native Swarm applications.

Swarm's configuration and status information is stored in a distributed etcd database located on all management nodes. The database runs in memory and keeps data up to date. The best thing about this database is that it requires almost no configuration, it is installed as part of Swarm and requires no administration.

Regarding cluster management, the biggest challenge is ensuring its security. When setting up a Swarm cluster you will inevitably use TLS as it is tightly integrated with Swarm.

In today's era of increasing security awareness, such a tool deserves to be vigorously promoted. Swarm uses TLS for communication encryption, node authentication, and role authorization. Automatic Key Rotation is the icing on the cake! It works silently in the background, and users don’t even notice the existence of this feature.

Regarding application orchestration, the smallest scheduling unit in Swarm is a service. It was introduced with Swarm and is a new object element in the API. It encapsulates some advanced features based on containers and is a higher-level concept. When a container is encapsulated in a service, we call it a task or a copy. Features such as expansion and contraction, rolling upgrade, and simple rollback are added to the service.

Recommended learning: "docker video tutorial"

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