Installing Docker Swarm

I have chosen to use CentOS 7 for my cluster of machines. So these instructions are for CentOS 7.

First I need to install docker on all of the machines in the cluster.

Set up yum so it can see the latest docker packages.

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

Next install docker onto each machine in your cluster.

# sudo yum install docker-ce

Once you have installed docker on every node in your cluster you can now set up your swarm. First you have to choose which machines will be your manager(s).

On one of the masters you need to initialize the swarm

# docker swarm init

If your machine has more than one network then you will need to specify the ip address to use for the master.

# docker swarm init --advertise-addr 172.16.0.100
Swarm initialized: current node (a2anz4z0mpb0vmcly5ksotfo1) is now a manager.
To add a worker to this swarm, run the following command:
docker swarm join \ --token SWMT....wns 172.16.0.100:2377
To add a manager to this swarm, run 'docker swarm join-token manager' and follow the instructions.

In this example the IP address is 172.16.0.100 for the swarm master. Now on each worker node I just run the join command as specified in the output of the init command.

# docker swarm join --token SWMT...wns 172.16.0.100:2377

If you want to add another master then you run the command

# docker swarm join-token manager

It will tell you exactly what you need to do.

Setting up Jenkins in your Swarm

Now this is the easy part. Sort of. With docker swarm and services this has just gotten much easier. There are several docker images that are available with jenkins already installed in them. So it is best if we just use one of them. The most popular is "jenkins". Go figure. Now with the image name all we need to do is start a service in the swarm. We can simply write a small compose file and we will be set.

# docker-jenkins.yaml
version: '3'
services:
jenkins:
image: jenkins
ports:
- "8082:8080"
- "50000:50000"
environment:
JENKINS_OPTS: --prefix=/jenkins
deploy:
placement:
constraints: [node.role == manager]
volumes:
- $PWD/docker/jenkins:/var/jenkins_home

There are a couple of things to note.

Ports - First the ports are mapped to 50000 and 8082. This are external ports and will be accessible outside of the container.
Environment - You can set any jenkins options on this line any following environment lines
Volumes - This will give us the ability to "mount" a directory from the host machine into the container. So if the container goes down we still have our jenkins installation. You will need to create the directory using

# mkdir ~/docker/jenkins && chmod 777 ~/docker/jenkins

if you don't do this you will have problems with jenkins coming up.

Now it is time to actually start the service.

# docker stack deploy -c docker-jenkins.yaml buildCreating network build_default
Creating service build_jenkins

Two things where created when the deploy was run. A default network "build_default" and the service "build_jenkins" notice all of the artifacts created will begin with "build_". The default network is created when a network is not specified.

Now you should be able to access the jenkins web site at

http://172.16.0.100:8082/jenkins

Jenkins now requires a password when you install. You can find the password in the secrets directory in the docker/jenkins base directory.

# cat ~/docker/jenkins/secrets/initialAdminPassord
asldfkasdlfkjlasdfj23iwrh

Cut and paste this into your browser and you will be set and ready to go.

Debugging Tools

Here are a couple of things I found useful when I was setting up the environment.

# docker ps

CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
91aa53f4642a jenkins@sha256:c0cac51cbd3af8947e105ec15aa4bcdbf0bd267984d8e7be5663b5551bbc5f4b "/bin/tini -- /usr..." 5 hours ago Up 5 hours 8080/tcp, 50000/tcp build_jenkins.1.abu55c8tybjwrsd35ouaor1d2

Shows the containers that are currently running. This will include the containers that are running the services. I found that some of the containers never started up. So I was trying to find out what happen. So I ran the following command:

# docker service ps build_jenkins

ID NAME IMAGE NODE DESIRED ST ATE CURRENT STATE ERROR PORTS
abu55c8tybjw build_jenkins.1 jenkins:latest node0.intel.local Running Running 5 hours ago
nac73zp1gc68 \_ build_jenkins.1 jenkins:latest node0.intel.local Shutdown Failed 5 hours ago "task: non-zero exit (1)"
xyrmzvx1pnnp \_ build_jenkins.1 jenkins:latest node0.intel.local Shutdown Failed 5 hours ago "task: non-zero exit (1)"
phycp5ypp61o \_ build_jenkins.1 jenkins:latest node0.intel.local Shutdown Failed 5 hours ago "task: non-zero exit (1)"
o3ewixv3hvcy \_ build_jenkins.1 jenkins:latest node0.intel.local Shutdown Failed 5 hours ago "task: non-zero exit (1)"

This will show the tasks for the services before the containers get launched and their status.

This last weekend I started cleaning out my garage. I said I started, because my garage will never completely be cleaned out. But I did manage to clean up my tool box. I found lots of interesting things in my tool box. Some broken tools, some tools that I have no idea how they got there. I am sure my neighbors and friends probably are missing them.

I also found half started projects that just got thrown in their that don't matter anymore. Probably in a hurry to clean up the mess in the garage. Anyway. I started thinking about all of these tools in my tool box, and of course comparing them to the tools I use at work. They are not things I can touch like the hardware in my tool box, but they are invaluable tools that I can use to get jobs done. I quickly broke down the tools into categories and found a group of tools that I have downloaded, played with and am using everyday that fit in the "Container Technology" category. So I gathered those tools together and decided to write this blog to help me keep track of what container tool to use for what job. This is what I have so far. Please note this is not a complete list, but a good start I think.

Container Tools

Docker - Container Definition and nice CLI to control Containers
Docker Compose - Define applications that contain more than one container.
Mesos - Meta-scheduler, Distribute Kernel
Docker Swarm - Container Scheduler that can talk to MesosS
Kubernetes - Container Scheduler that can schedule and control Containers.
Marathon - Service based scheduler for containers. Plugin to Mesos
Chronos - Temporal Based Scheduler for containers. Plugin to Mesos

This is how I see everything fitting together.

Docker (Production - 1.7.0)

This helps developers define how to configure a container. Starts with a base image and then allows you to run commands, expose ports, and copy data into the container through a simple configuration file. Docker also gives CLI and REST API to allow users to control the individual containers. It requires a Docker controller running on a physical or virtual machine.

Docker Compose (Beta - 1.7.0)

Gives developers the ability to define an application as a set of micro-services. It shows the dependencies between the micro-services (containers). Which ports they expose to each other, their startup order, and any shared resources(data) between the containers that make up the application.

Mesos (Production - 0.23.0)

"A distributed systems kernel" from the mesos web site.

Mesos describes itself as a distributed system kernel. It is responsible for picking physical compute nodes to run containers, jobs, micro-services, etc... I gets telemetry from the physical hardware and can determine which machines can best handle incoming jobs. It then provisions machines and executes job on those machines. Schedulers like Kubernetes, Marathon, Chronos, and Docker Swarm sit ontop of Mesos and act as the orchestrator for the containers running in the cloud.

Schedulers

Docker Swarm (Still in Alpha - 0.3.0 )

If you want to use a familiar Docker API you can use Docker Swarm with Mesos to control multiple containers on mutilple hosts. There is rumor it may also allow you to talk to Kubernetes in the future. Check out http://www.techrepublic.com/article/docker-and-mesos-like-peanut-butter-and-jelly/ for more information.

Kubernetes ( pre-production Beta - 0.19.0 )

If you want to launch groups of containers (K8 Pods) co-scheduled and co-located together, sharing resources on the same machine.
If you want to launch a service alongside one or more sidekick containers (e.g. log archiver, metrics monitor) that live next to the parent container.
if you want to use the K8s label-based service-discovery, load-balancing, and replication control. Very cool stuff for managing large number of containers.
If you want to manage groups of containers(K8 Pods).
If you want to load balance in isolation (K8 Pods).

Marathon (Production - 0.8.2)

If you want to launch applications that contain long running heterogeneous apps/services (Docker and Non-Docker).
If you want to use Mesos attributes for constraint-based scheduling.
If you want to use application groups and dependencies to launch, scale, or upgrade related services.
If you want to use event driven health checks to automatically restart unhealthy services.
If you want to integrate HAProxy or Consul for service discovery.
If you want a nice web UI or REST API to launch and monitor apps.

Chronos (Production - 2.3.4)

If you want to launch applications that contain short running heterogeneous apps/services (Docker and Non-Docker).
If you want to schedule a remporal task to run at a specific time/schedule, just like cron.
If you want to schedule a DAG workflow of dependent tasks.
If you want a nice web UI or REST API to launch and monitor apps.
If you want to use a scheduler that was built from the start with Mesos in mind.

Ok. This is the start. I am sure many of you have more to add to the list. Please let me know what I am missing.

DWP.

Yoly Software Engineering

Tuesday, April 11, 2017

Fault Tolerance Jenkins with Docker Swarm