Create a Docker Swarm Manager and Nodes on Linode

If the last manager
node leaves the swarm, the swarm becomes unavailable requiring you to take
disaster recovery measures. This is useful when a
manager node becomes unavailable or if you want to take a manager offline for
maintenance. For instance, an engine could have a label to indicate
that it has a certain type of disk device, which may not be relevant to security
directly.

¹Its now 2022 and the next version of Docker has not yet gone live with CSI support. You may wish to consult the following resources for additional information
on this topic. While these are provided in the hope that they will be
useful, please note that we cannot vouch for the accuracy or timeliness of
externally hosted materials. By executing the above command, you can access the HelloWorld file from the remote system.

How nodes work

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. If you are using Linux based physical computers or cloud-provided computers as
hosts, simply follow the Linux install instructions
for your platform. You can test both
single-node and multi-node swarm scenarios on Linux machines. We can use Docker Swarm to make Docker work across multiple nodes, allowing them to share containers with each other.

Worker nodes are responsible for executing tasks that dispatch to them from manager nodes. An agent runs on each worker node and reports to the manager node on its assigned tasks. It helps the manager node to maintain the desired state of each worker node. A task is work to be done, and service is a description of that task or the state. Once a task is assigned to a particular node, we cannot assign it to another node.

Create and manage access tokens

In Docker Swarm mode, each node is a Docker daemon (used to run Docker on the system), and all these Docker daemons interact with each other using the Docker API. Additionally, we can deploy each container within the Swarm, and nodes of the same cluster can access them. Now, you need to copy and run the full command you get in the output of ‘docker swarm join-token worker’ in your worker node to join the Swarm. The manager node then uses the scheduler to assign and reassign tasks to nodes as required and specified in the Docker service. Typically though, nodes span over several computers and servers running the Docker engine in real-life applications. And as mentioned earlier, a node can either be a manager or worker node, depending on the role.

When you run a service, it compels the manager node to sync with its configurations. The manager node then runs the rest of the worker nodes based on the specified settings in the service. When you have multiple managers you can recover
from the failure of a manager node without downtime. All nodes in the swarm route ingress
connections to a running task instance. In the next step of
the tutorial, you
deploy a service to the swarm.

Inspect an individual node

A task carries a Docker container as well as the commands to run inside this container. Depending on the number of replicas set on the service scale, the manager node assigns tasks to worker nodes. Note that once a task gets assigned to a particular node, it cannot move to another node. As shown in the above figure, a Docker Swarm environment has an API that allows us to do orchestration by creating tasks for each service.

• When you interact with Docker Hub using the Docker CLI, the CLI uses this token for authentication.
• The internal IP addresses used by Docker can be changed from Settings.
• Invariably, the worker nodes receive task allocation from the manager node and execute them accordingly.
• When you have multiple managers you can recover
  from the failure of a manager node without downtime.
• Here first, we create a Swarm cluster by giving the IP address of the manager node.
• A Docker Swarm is a group/ cluster of machines (either physical or virtual) that run the Docker application and configure it to join together in a cluster.

All our containers will be inaccessible and cause many issues so we have docker-swarm mode architecture to deploy docker in a production environment. It enables you to deploy and manage a group of containers across multiple hosts, providing load balancing, scaling, and high availability for your applications. A node is an instance of the Docker engine participating in the swarm cluster. One or more nodes can execute on a single physical machine or cloud server. Still, in an actual production swarm environment, we have Docker nodes distributed across multiple physical and cloud machines.

Getting started with swarm mode

Worker nodes receive and execute tasks dispatched from manager nodes. By default manager nodes also run services as worker nodes, but you can
configure managed docker swarm them to run manager tasks exclusively and be manager-only
nodes. An agent runs on each worker node and reports on the tasks assigned to
it.

When an application deploys to a swarm, we submit a service definition to a manager node. The manager node then dispatches units of work or tasks to worker nodes. The manager node is also responsible for orchestration and cluster management function that helps maintain the swarm’s desired state. You can create a swarm of one manager node, but you cannot have a worker node
without at least one manager node. In a single manager node cluster, you can run commands like docker service create and the scheduler places all tasks on the local Engine. 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.

What Is Docker Swarm Mode and How Does It Work?

If you plan on creating an overlay network with encryption (–opt encrypted),
you also need to ensure IP protocol 50 (IPSec ESP) traffic is allowed. You can run ifconfig on Linux or macOS to see a list of the
available network interfaces. This tutorial uses Docker Engine CLI commands entered on the command line of a
terminal window. See the
run command for more details on
publish options used with docker run.

If you’ve been containerizing your development workflow, you’ll agree that Docker is one of the best choices for version control. However, Docker Swarm is one of Docker’s features used to orchestrate complex apps. Port 4789 is the default value for the Swarm data path port, also known as the VXLAN port. It is important to prevent any untrusted traffic from reaching this port, as VXLAN does not
provide authentication. This port should only be opened to a trusted network, and never at a
perimeter firewall.

Create a Docker Swarm Manager and Nodes on Linode

Keep reading for details about concepts related to Docker swarm services,
including nodes, services, tasks, and load balancing. Once you’ve
created a swarm with a manager node, you’re ready
to add worker nodes. This is the basic architecture of docker-swarm here we have one manager node and 2 worker nodes.