Get started Part4 : swarms¶
Contents
Introduction¶
In part 3, you took an app you wrote in part 2, and defined how it should run in production by turning it into a service, scaling it up 5x in the process.
Here in part 4, you deploy this application onto a cluster, running it on multiple machines.
Multi-container, multi-machine applications are made possible by joining multiple machines into a Dockerized cluster called a swarm.
Understanding Swarm clusters¶
A swarm is a group of machines that are running Docker and joined into a cluster. After that has happened, you continue to run the Docker commands you’re used to, but now they are executed on a cluster by a swarm manager.
The machines in a swarm can be physical or virtual. After joining a swarm, they are referred to as nodes.
Swarm managers can use several strategies to run containers, such as emptiest node – which fills the least utilized machines with containers. Or global, which ensures that each machine gets exactly one instance of the specified container. You instruct the swarm manager to use these strategies in the Compose file, just like the one you have already been using.
Swarm managers are the only machines in a swarm that can execute your commands, or authorize other machines to join the swarm as workers. Workers are just there to provide capacity and do not have the authority to tell any other machine what it can and cannot do.
Up until now, you have been using Docker in a single-host mode on your local machine. But Docker also can be switched into swarm mode, and that’s what enables the use of swarms. Enabling swarm mode instantly makes the current machine a swarm manager. From then on, Docker will run the commands you execute on the swarm you’re managing, rather than just on the current machine.
Set up your swarm¶
A swarm is made up of multiple nodes, which can be either physical or virtual machines. The basic concept is simple enough: run docker swarm init to enable swarm mode and make your current machine a swarm manager, then run docker swarm join on other machines to have them join the swarm as workers.
Choose a tab below to see how this plays out in various contexts. We’ll use VMs to quickly create a two-machine cluster and turn it into a swarm.
Encore Bloqué¶
PS C:/WINDOWS/system32> docker-machine create -d hyperv --hyperv-virtual-switch "myswitch" myvm1
PS C:/WINDOWS/system32> docker-machine create -d hyperv --hyperv-virtual-switch "myswitch" myvm1
Creating CA: C:/Users/compadm/.docker/machine/certs/ca.pem
Creating client certificate: C:/Users/compadm/.docker/machine/certs/cert.pem
Running pre-create checks...
(myvm1) Image cache directory does not exist, creating it at C:/Users/compadm/.docker/machine/cache...
(myvm1) No default Boot2Docker ISO found locally, downloading the latest release...
(myvm1) Latest release for github.com/boot2docker/boot2docker is v18.01.0-ce
(myvm1) Downloading C:/Users/compadm/.docker/machine/cache/boot2docker.iso from https://github.com/boot2docker/boot2dock
er/releases/download/v18.01.0-ce/boot2docker.iso...
Error with pre-create check: "Get https://github-production-release-asset-2e65be.s3.amazonaws.com/14930729/634fb5b0-f6ac-11e7-8f12-e1c4544a979b?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=A
KIAIWNJYAX4CSVEH53A%2F20180115%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20180115T134730Z&X-Amz-Expires=300&X-Amz-Signature=5efdfe365c94b790f1a95579a7f424a0731be82a19a2d806340d18c5608577be&X-Amz
-SignedHeaders=host&actor_id=0&response-content-disposition=attachment%3B%20filename%3Dboot2docker.iso&response-content-type=application%2Foctet-stream: read tcp 10.0.40.41:55806->54.231.48.184:4
43: wsarecv: Une tentative de connexion a échoué car le parti connecté n’a pas répondu convenablement au-delà d’une certaine durée ou une connexion établie a échoué car l’hôte de connexion n’a pa
s répondu."
Warning
impossible d’accéder au stockage Amazon S3.
