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This article is about how Docker deploys Swarm. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

About Docker Swarm

Docker Swarm consists of two parts:

Docker cluster: one or more Docker nodes are organized so that users can manage them in a cluster manner

Application choreography: there is a set of API for deploying and managing containers

Official Information: https://docs.docker.com/swarm/

Network diagram

The following figure is a typical Docker Swarm cluster deployment diagram from the Docker official website:

Next, follow the figure above to build a Docker Swarm cluster.

Preparatory work

A total of 5 machines are used in this actual combat, and the configuration information is all the same, as follows:

Operating system: CentOS Linux release 7.6.1810

Docker Service version: 1.13.1

The firewalls are off.

The information for the machine is shown in the following table:

IP address hostname identity 192.168.121.142m0 management node 192.168.121.139m1 management node 192.168.121.140m2 management node 192.168.121.141w0 work node 192.168.121.138w1 work node

Why three management nodes?

As can be seen from the official chart, the Raft consensus algorithm is used for internal management coordination between management node clusters, which ensures the high availability of management nodes (HA). In general, the following two principles will be referred to:

Deploy an odd number of management nodes, which helps to reduce brain fissure

Don't deploy too many management nodes, because more management nodes means it takes more time to reach a consensus

Introduction to the steps of deploying a cluster

The entire deployment process is divided into the following steps:

Initialize the first management node (M0)

Add a new management node (M1, m2)

Join the work node (W0, W1)

Next, let's officially begin.

Initialize the first management node (M0)

The IP address of the M0 node is 192.168.121.142, so execute the following command on the M0 node:

Docker swarm init\-- advertise-addr 192.168.121.142:2377--listen-addr 192.168.121.142pur2377

With regard to the parameters advertise-addr and listen-addr, the former is used to specify the address when other nodes connect to m0, while the latter specifies the IP and port that carry swarm traffic. For more detailed and in-depth differences between them, please refer to the article: https://boxboat.com/2016/08/17/whats-docker-swarm-advertise-addr/

two。 The returned information from the console is as follows, indicating that the Swarm cluster was initialized successfully:

Swarm initialized: current node (7585zt09o2sat82maef0ocf42) is now a manager.To add a worker to this swarm, run the following command: docker swarm join\-token SWMTKN-1-5huefb5501cv7p8i2op1am2oevasoqu4te8vpvapndkudvszb4-e8l6755jstd7urpdo5smyi8fv\ 192.168.121.142:2377To add a manager to this swarm, run 'docker swarm join-token manager' and follow the instructions.

Listing all the nodes in the current Swarm cluster, you can see the status and identity of the unique node m0:

[root@m0 ~] # docker node lsID HOSTNAME STATUS AVAILABILITY MANAGER STATUS7585zt09o2sat82maef0ocf42 * M0 Ready Active Leader

Now that the cluster has been set up, we need to add more management nodes and work nodes

How to add a new node?

Docker Swarm's new node joining strategy is to get a long list of commands from the management node, called join token. Any machine that wants to join the cluster can join the Swarm cluster as long as it executes the join token.

If a new management node needs to be joined, execute the command docker swarm join-token manager at M0 to get the join token of the management node, as shown below:

[root@m0] # docker swarm join-token managerTo add a manager to this swarm, run the following command: docker swarm join\-- token SWMTKN-1-5huefb5501cv7p8i2op1am2oevasoqu4te8vpvapndkudvszb4-5tz9d4w7nwzu8r4ozd0ff2aiu\ 192.168.121.142Vol 2377

If a new worker node needs to be joined, execute the command docker swarm join-token worker in M0 to get the join token of the worker node, as shown below:

[root@m0 ~] # docker swarm join-token workerTo add a worker to this swarm, run the following command: docker swarm join\-- token SWMTKN-1-5huefb5501cv7p8i2op1am2oevasoqu4te8vpvapndkudvszb4-e8l6755jstd7urpdo5smyi8fv\ 192.168.121.142VR 2377

Both types of join token are ready, and then start adding new nodes.

Join the management nodes M1, m2

Execute the previously obtained management node join token on M1:

[root@m1] # docker swarm join\ >-- token SWMTKN-1-5huefb5501cv7p8i2op1am2oevasoqu4te8vpvapndkudvszb4-5tz9d4w7nwzu8r4ozd0ff2aiu\ > 192.168.121.142:2377This node joined a swarm as a manager.

Do the same operation on m2

Execute the command docker node ls on any one of M0, M1, m2 to view the status of the Swarm cluster. As shown in the figure below, the three management nodes are all normal. The ID field with an asterisk suffix indicates that the machine currently executing the command is M1:

[root@m1 ~] # docker node lsID HOSTNAME STATUS AVAILABILITY MANAGER STATUS0isfyre69mdu1hm11esf1q3dk m2 Ready Active Reachable7585zt09o2sat82maef0ocf42 M0 Ready Active Leaderslc0hjbs7jh3hdi8ai3wohy23 * M1 Ready Active Reachable

Join the work nodes W0 and W1

Execute the join token of the previously obtained worker node on w0:

[root@w0] # docker swarm join\ >-- token SWMTKN-1-5huefb5501cv7p8i2op1am2oevasoqu4te8vpvapndkudvszb4-e8l6755jstd7urpdo5smyi8fv\ > 192.168.121.142:2377This node joined a swarm as a worker.

Do the same thing on W1

Execute the command docker node ls on any one of M0, M1, m2 to view the status of the Swarm cluster, and you can see that the work nodes are all ready:

[root@m0 ~] # docker node lsID HOSTNAME STATUS AVAILABILITY MANAGER STATUS0isfyre69mdu1hm11esf1q3dk m2 Ready Active Reachable7585zt09o2sat82maef0ocf42 * M0 Ready Active Leaderi71bcxt1auc804syybroajtan w1 Ready Active slc0hjbs7jh3hdi8ai3wohy23 M1 Ready Active Reachablewqcwcccva3d3mxgi5p423d4fv w0 Ready Active

At this point, the Swarm cluster environment is built, and then you can verify it.

Verify the Swarm cluster environment

Create an overlay network (Overlay Netowork) called tomcat-net, which is a layer 2 network under which docker containers can access each other even if the host is different:

Docker network create-d overlay tomcat-net

Create a service called tomcat that uses the overlay network you just created:

Docker service create-- name tomcat\-- network tomcat-net\-- p 8080Viru 8080\-- replicas 3\ tomcat:7.0.96-jdk8-openjdk

Execute the command docker service ls to view all current services:

[root@m0 ~] # docker service lsID NAME MODE REPLICAS IMAGEkguawc4b5th5 tomcat replicated 3amp 3 tomcat:7.0.96-jdk8-openjdk

Execute the command docker service ps tomcat to view the service named tomcat. You can see that the three containers are deployed on M0, m2, and W1 machines respectively:

[root@m0 ~] # docker service ps tomcatID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTSn1gs9f1plce2 tomcat.1 tomcat:7.0.96-jdk8-openjdk W1 Running Running 19 minutes ago q8jyg088ci21 tomcat.2 tomcat:7.0.96-jdk8-openjdk m2 Running Running 19 minutes ago h9ww33dpw56m tomcat.3 tomcat:7.0.96-jdk8-openjdk M0 Running Running 19 minutes ago

Execute the command docker service inspect-- pretty tomcat to view the details of the service named tomcat (remove-pretty to see a more complete one):

[root@m0 ~] # docker service inspect-- pretty tomcatID: kguawc4b5th5qlwlsv183qtaiName: tomcatService Mode: Replicated Replicas: Parallelism: 1 On failure: pause Max failure ratio: 0ContainerSpec: Image: tomcat:7.0.96-jdk8-openjdk@sha256:91eadffb59d9a35ada2d39fcd616a749ac580aa5e834499b7128f27be2e46623Resources:Networks: tomcat-net Endpoint Mode: vipPorts: PublishedPort 8080 Protocol = tcp TargetPort = 8080

Open a browser and try to access port 8080 of the five machines: M0, M1, m2, W0, and W1. You can successfully access the home page of tomcat:

Service model

There are two service modes: Ingress and Host. If not specified, the default is Ingress.

In Ingress mode, traffic to port 8080 of any Swarm node is mapped to the internal port 80 of any service replica, even if there is no tomcat service copy on that node.

In Host mode, the port is opened only on machines running a copy of the container. The command to use Host mode is as follows:

Docker service create-name tomcat\-network tomcat-net\-publish published=8080,target=8080,mode=host\-replicas 3\ tomcat:7.0.96-jdk8-openjdk

Service expansion and reduction

Execute the command docker service scale tomcat=5 to adjust the number of copies from 3 to 5:

[root@m0 ~] # docker service scale tomcat=5tomcat scaled to 5

Execute the command docker service ps tomcat to view the service named tomcat, and you can see that there is a container distributed on each machine:

[root@m0] # docker service ps tomcatID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTSw32tjahze2fk tomcat.1 tomcat:7.0.96-jdk8-openjdk m2 Running Running 42 minutes ago yj5czwwhrrsh tomcat.2 tomcat:7.0.96-jdk8-openjdk M0 Running Running 42 minutes ago pq40995nbd0k tomcat.3 tomcat:7.0.96-jdk8-openjdk w1 Running Running 42 minutes ago y1y6z1jczel1 tomcat.4 tomcat:7.0.96-jdk8-openjdk M1 Running Running about a minute ago w0dcii8f79os tomcat.5 tomcat:7.0.96-jdk8-openjdk w0 Running Running about a minute ago

Rolling upgrade

In the current tomcat service, the tag of tomcat image is 7.0.96-jdk8-openjdk. Let's try to upgrade to 9.0.24-jdk11-openjdk and execute the following command:

Docker service update\-- image tomcat:9.0.24-jdk11-openjdk\-- update-parallelism 1\-- update-delay 10s tomcat

There are several points to be noted in the above order:

A. update-parallelism: the number of containers updated each time, which is set to 1 here, which means that each container will be upgraded successfully before upgrading the next one.

B. update-delay: the waiting time before upgrading the next batch after each batch is upgraded successfully. Here, wait 10 seconds after upgrading one container before upgrading the next one.

two。 When you execute the command docker service ps tomcat to view the service during the upgrade, you can see the process of starting the new version container one by one:

[root@m0] # docker service ps tomcatID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTSw32tjahze2fk tomcat.1 tomcat:7.0.96-jdk8-openjdk m2 Running Running 56 minutes ago yj5czwwhrrsh tomcat.2 tomcat:7.0.96-jdk8-openjdk M0 Running Running 56 minutes ago semuna9awsn7 tomcat.3 tomcat:9.0.24-jdk11-openjdk W1 Running Running 15 seconds ago pq40995nbd0k\ _ tomcat.3 tomcat:7. 0.96-jdk8-openjdk W1 Shutdown Shutdown about a minute ago y1y6z1jczel1 tomcat.4 tomcat:7.0.96-jdk8-openjdk M1 Running Running 15 minutes ago oot3yex74v4t tomcat.5 tomcat:9.0.24-jdk11-openjdk W0 Running Preparing 5 seconds ago w0dcii8f79os\ _ tomcat.5 tomcat:7.0.96-jdk8-openjdk W0 Shutdown Shutdown 3 seconds ago

After the upgrade is completed, access the service with a browser, which shows that the tomcat version has been upgraded:

Delete a service

Execute the command docker service rm tomcat to delete the service:

[root@m0] # docker service rm tomcattomcat [root@m0 ~] # docker service lsID NAME MODE REPLICAS IMAGE Thank you for reading! This is the end of the article on "how Docker deploys Swarm". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, you can share it for more people to see!

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