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6_Building_the_Nomad_Agent_Cluster.md

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Chapter 5 - Building the Nomad Client Cluster

Prerequisites

  • A XenServer 7.2 Environment
  • XenCenter 7.2
  • the centos-7-small template as built in Chapter 1.
  • a three-node Consul cluster as built in Chapter 2
  • a two-node Vault cluster as built in Chapter 3 (optional)
  • a three-node Nomad server cluster as built in Chapter 4
  • a workstation with the following

Process

  • Terraform the Nomad agent nodes.
  • Install the Consul agent on the nodes.
  • Configure Nomad Service
  • Install Docker
  • Run a sample job

Goal

By the time we have completed this section, you will have a fully functional Nomad Cluster configured to take advantage of Consul for service registration and discovery, and will have run the sample Redis job against the cluster to test Vault integration

Terraform Nomad client nodes

Create a project directory that will hold your terraform files and states. Since I would like to be able to provision and destroy each infrastructure component individually, I have a subfolder in my project directory for Consul, Vault, and Nomad.

└── play_cluster
    ├── consul
    ├── nomad-server
    ├── nomad-client
    └── vault

Switch to your nomad-client folder.

Create the nomad-client.tf file

Create a nomad-client.tf file with the following information. Replace placeholders in "«»" with appropriate values from your environment.

provider "xenserver" {
    url = "«XenServer URL»"
    username = "«XenServer user name»"
    password = "«XenServer password»"
}

resource "xenserver_vm" "nomad-client-1" {
    name_label = "nomad-client-1"
    base_template_name = "centos-7-small"
    xenstore_data {
      hostname = "nomad-client-1.node.consul"
    }
}

resource "xenserver_vm" "nomad-client-2" {
    name_label = "nomad-client-2"
    base_template_name = "centos-7-small"
    xenstore_data {
      hostname = "nomad-client-2.node.consul"
    }
}

resource "xenserver_vm" "nomad-client-3" {
    name_label = "nomad-client-3"
    base_template_name = "centos-7-small"
    xenstore_data {
      hostname = "nomad-client-3.node.consul"
    }
}

At this point, you should be able to run terraform plan and see that three resources will be created.

Run terraform apply to build your three nodes.

Install Consul Agent

See Appendix C - Installing Consul Agent and Configuring DNS Integration

Install Nomad

Write Nomad Client Configuration

cat << NOMADCONFIG | sudo tee /etc/nomad.d/nomad.hcl
datacenter = "dc1"
data_dir = "/opt/nomad/data"
log_level = "DEBUG"
leave_on_interrupt = true

client {
  enabled = true
}
NOMADCONFIG

Make firewalld rules for nomad

sudo firewall-cmd --zone=public --permanent --add-port=4646/tcp
sudo firewall-cmd --zone=public --permanent --add-port=4647/tcp
sudo firewall-cmd --zone=public --permanent --add-port=4648/tcp
sudo firewall-cmd --zone=public --permanent --add-port=4648/udp
sudo firewall-cmd --reload

cat << NOMADSRVSERVICE | sudo tee /etc/systemd/system/nomad.service
[Unit]
Description=Nomad
Requires=network-online.target
After=network-online.target

[Service]
User=root
EnvironmentFile=-/etc/sysconfig/nomad
Environment=GOMAXPROCS=2
Restart=on-failure
ExecStart=/usr/local/bin/nomad agent \$OPTIONS -config=/etc/nomad.d/nomad.hcl
ExecReload=/bin/kill -HUP \$MAINPID
KillSignal=SIGINT
StandardOutput=journal+console

[Install]
WantedBy=multi-user.target
NOMADSRVSERVICE

Note: If the nomad-client service unit will not stay running and running the nomad command by hand gives you the following error:

==> Failed to parse HTTP advertise address: No valid advertise addresses, please set `advertise` manually

you need either add an advertise entry to the configuration or configure a hosts file entry that maps the nodes name to an IP address.

Install Docker for the Sample Job

The sample job created with nomad init requires that Docker be installed on the Nomad client machines. You can fetch and run the installer with this one-liner.

curl -fsSL https://get.docker.com/ | sh

Once docker is installed, you will need to add the nomad user to the docker group

sudo usermod -aG docker nomad

Start docker and enable it to run on boot.

sudo systemctl start docker
sudo systemctl enable docker

Verify that docker is running as expected.

sudo systemctl status docker

Start the Nomad client service

sudo systemctl enable nomad.service
sudo systemctl start nomad.service

Create and run a sample job

At this point, you should have three Consul client members in your cluster.

From your workstation, connect to nomad-server-1 as the nomad user. Run nomad init to generate the example job. Run nomad run example.nomad to submit the job to the cluster. Check to see if the job has started using nomad status example. You can also verify this in your Consul Web UI by looking for the global-redis-check service to show on the services page.