C_Installing_Consul_Agent.md

Appendix C - Installing Consul Agent and Configuring DNS Integration

Install Consul Agent

You can perform these steps on one node at a time or on multiples at once using a tool like cssh (csshX on macOS)

Create the consul user

useradd consul
sudo mkdir -p /etc/consul.d
sudo chown consul /etc/consul.d
sudo mkdir -p /opt/consul/data
chown -R consul /opt/consul
passwd consul

Configure the node name

hostnamectl set-hostname $(xenstore-read vm-data/hostname)
echo "$(hostname -I) $(xenstore-read vm-data/hostname) " >> /etc/hosts

Install Bind and Configure Consul DNS Integration

yum install -y bind bind-utils

sudo cp /etc/named.conf /etc/named.conf.orig

echo 'include "/etc/named.consul.conf";' | sudo tee -a /etc/named.conf

sudo sed -i 's/dnssec-enable yes/dnssec-enable no/g' /etc/named.conf

sudo sed -i 's/dnssec-validation yes/dnssec-validation no/g' /etc/named.conf

cat << CONSULCONF | sudo tee /etc/named.consul.conf
zone "consul" IN {
  type forward;
  forward only;
  forwarders { 127.0.0.1 port 8600; };
};
CONSULCONF

sudo systemctl start named
sudo systemctl enable named

Edit resolv.conf and configure name resolution to use your newly installed local DNS server.

cat << RESOLVCONF | sudo tee /etc/resolv.conf
search node.consul
nameserver 127.0.0.1
RESOLVCONF

Write Consul Configuration

Note: If performing this step on more than one node at a time, make sure that you have the node name correct in this file.

I am using jq (https://stedolan.github.io/jq/) to query the Consul cluster for configuration information to be used in configuring the consul agent. This could be done in a more manual fashion, but this facilitates the use of cssh or csshX to provision nodes.

wget https://github.com/stedolan/jq/releases/download/jq-1.5/jq-linux64
mv jq-linux64 /usr/local/bin/jq
chmod +x /usr/local/bin/jq

export CONSUL_IP=10.0.2.21
export CONSUL_IPS=$(curl -s http://$CONSUL_IP:8500/v1/catalog/service/consul | jq --compact-output '[.[] | .Address]')
export NODENAME_SHORT=$(xenstore-read vm-data/hostname | cut -f1 -d.)
export HOST_IP=$(hostname -I| tr -d " ")

cat << CONSULCONFIG | sudo tee /etc/consul.d/config-agent.json
{
  "retry_join": $CONSUL_IPS,
  "bind_addr": "$HOST_IP",
  "client_addr": "0.0.0.0",
  "datacenter": "dc1",
  "data_dir": "/opt/consul/data",
  "log_level": "INFO",
  "node_name": "$NODENAME_SHORT",
  "watches": [
  ]
}
CONSULCONFIG
sudo chown consul /etc/consul.d/config-agent.json

Note: We have to configure bind_addr in the configuration or Consul will fail to start after docker is installed because it will no longer be able to determine what address to advertise.

Create the systemd service definition

cat << CONSULSERVICE | sudo tee /etc/systemd/system/consul-agent.service
[Unit]
Description=Consul Agent
Requires=network-online.target
After=network-online.target

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

[Install]
WantedBy=multi-user.target
CONSULSERVICE

Make firewalld rules for consul

sudo firewall-cmd --zone=public --permanent --add-port=8301/tcp
sudo firewall-cmd --reload

Enable and start the consul-agent service

sudo systemctl enable consul-agent.service
sudo systemctl start consul-agent.service