How to stop the Docker Swarm Manager to act as Worker

Posted on April 13, 2018April 13, 2018 by Aghassi

Docker Swarm Manager act as Worker too?

Yes, by default all managers acts as worker nodes.Main reason is, in a single manager node cluster, you can run commands like docker service create and the scheduler will place all tasks on the local Engine.

How to stop the Docker Swarm Manager to act as Worker?

To prevent the scheduler from placing tasks on a manager node in a multi-node swarm, set the availability for the manager node to Drain. The scheduler gracefully stops tasks on nodes in Drain mode and schedules the tasks on an Active node. The scheduler does not assign new tasks to nodes with Drain availability.

# docker node update --availability drain <ManagerNode>

Create and Manage Swarm Services

Posted on April 11, 2018April 13, 2018 by Aghassi

Swarm Service

Service is the definition of the tasks to execute on the worker nodes. It is the central structure of the swarm system and the primary root of user interaction with the swarm. When you create a service, you specify which container image to use and which commands to execute inside running containers.

Running Services in the Docker Swarm

We have swarm cluster up and we are ready to deploy the services. In this demo we will deploy service name “webserver” which will be using “nginx” docker images.

# docker service create -p 8080:80 --name webserver nginx

In the above example, we’re mapping port 80 in the Nginx container to port 8080 on the cluster so that we can access the default nginx page from anywhere.

Swarm Service modes

Swarm service support 2 modes – Replicated and Global (Replicated mode is default)

Replicated mode – you can pass number of replica of the service and swarm maintain that count.

# docker service create --name replicated_service --replicas 3 nginx

Global mode – To start a global service on each available node, pass –mode global to docker service create. Every time a new node becomes available, the scheduler places a task for the global service on the new node.

# docker service create --name global_service --mode global nginx

To view services on a cluster

# docker service ls

# docker service inspect --pretty <ServiceNAME|ServiceID>

To determine which nodes the services is running on by using docker service ps followed by service name

# docker service ps <ServiceNAME|ServiceID>

Docker by default use mesh networking, a service running on a node can be accessed on any other node of the cluster.

Scale Up/Down the Service

# docker service scale <ServiceNAME>=<#ofReplicas>

Remove a Service

# docker service rm <ServiceNAME|ServiceID>

Create Docker Swarm

Posted on April 10, 2018April 11, 2018 by Aghassi

Docker Swarm

Swarm is native clustering for the Docker. When the Docker Engine runs is swarm mode, manager nodes implement the Raft Consensus Algorithm to manage the global cluster state. The reason why Docker swarm mode is using a consensus algorithm is to make sure that all the manager nodes that are in charge of managing and scheduling tasks in the cluster, are storing the same consistent state.

LAB Setup

In this LAB we are going to create a Swarm cluster with single manager and 2 worker nodes.

Operating System	CentOS 7.4 x86_64
Platform	Vagrant Machines

Manager Node	manager	192.168.11.100/24
Worker Node 1	node-1	192.168.11.101/24
Worker Node 2	node-2	192.168.11.102/24

Prerequisites

Docker Engine 1.12 or later installed. We are going to install “ce” (community engine)

# yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo

# yum install docker-ce -y

# systemctl start docker.service

# systemctl enable docker.service

Static IP address of the manager machine, preferably for all machines
Network connectivity between all nodes and manager
Following Open Network ports

TCP port 2377 for cluster management communications

TCP and UDP port 7946 for communication among swarm nodes

UDP port 4789 for overlay network traffic

Create a Swarm

After the installation of the docker engine, next step is to enable the swarm mode, by default it is disabled.

Step-1: Initialize the Swarm

To crate a new swarm run the below command on the manager node.

# docker swarm init --advertise-addr 192.168.11.100

This command switches the current node into swarm mode and creates a new swarm. On the node where swarm init is done, that node is designated as manager node and it starts on listening on the advertised IP address over port 2377.

With swarm init – by default, generates tokens for worker and manager nodes to join the swarm, you can regenerate the tokens again, if missed to node those.