Consul Events

Demo

Consul must first be installed and configured using the Getting Started guide on consul.io
There are also other checks that I had to do on my own including health checks and registering services before
this was up and running properly. I initially started to use Atlas, a nice UI interface, to test and show stats
but the team decided against that method for now.

All these represent AWS EC2 node instances
Run on the server node:
    [root@ip-10-168-16-98 pearson]# consul agent -server -bootstrap-expect 1 -data-dir /tmp/consul -node=server-boss -bind=10.168.16.98

You should see this message from the server node:     
    2015/03/05 17:05:49 [INFO] consul: cluster leadership acquired
    2015/03/05 17:05:49 [INFO] consul: New leader elected: server-boss

Run on first agent:
    [root@ip-10-168-18-181 pearson]# consul agent -data-dir /tmp/consul -node=agent-two -bind=10.168.18.181

Run again on another server if you would like to connect another agent:
    [root@ip-10-168-15-13 pearson]# consul agent -data-dir /tmp/consul -node=agent-three -bind=10.168.15.13

Connect the Servers using the server node. Do this until all agents are connected
    [pearson@ip-10-168-16-98 ~]$ consul join 10.168.15.13
AND
    [pearson@ip-10-168-16-98 ~]$ consul join 10.168.18.181
    Successfully joined cluster by contacting 1 nodes.

You should see a message similar to this on the agent side once the server begins to join the agents:
    2015/03/05 17:15:09 [INFO] serf: EventMemberJoin: agent-two 10.168.18.181
    2015/03/05 17:15:09 [INFO] serf: EventMemberJoin: server-boss 10.168.16.98
    2015/03/05 17:15:09 [INFO] serf: EventMemberJoin: agent-four 10.168.18.239
    2015/03/05 17:15:09 [INFO] serf: EventMemberJoin: agent-three 10.168.15.13
    2015/03/05 17:15:09 [INFO] consul: adding server server-boss (Addr: 10.168.16.98:8300) (DC: dc1)
    2015/03/05 17:15:09 [INFO] consul: New leader elected: server-boss
Notice that each server, whether server or agent, joins the group and 'gossips.'

Type the command 'consul members' and you should see all the connections:
    [pearson@ip-10-168-16-98 ~]$ consul members
    Node         Address             Status  Type    Build  Protocol
    server-boss  10.168.16.98:8301   alive   server  0.5.0  2
    agent-three  10.168.15.13:8301   alive   client  0.5.0  2
    agent-two    10.168.18.181:8301  alive   client  0.5.0  2
    agent-four   10.168.18.239:8301  alive   client  0.5.0  2
    agent-five   10.168.19.71:8301   alive   client  0.5.0  2
This command can be used on any connected agent or server.

I placed a shell script in /usr/bin/ that would execute if a particular event happened:
    [root@ip-10-168-16-98 pearson]# consul watch -type event -name web-deploy /usr/bin/my-deploy-handler.sh &
    [1] 16798 -> pid
Notice I am running this in the background so I can use the same terminal. I don't care about the output
This 'watch' is being run on the main server in this example. The shell script spits out a .txt file in the server's
home directory. The name of the 'event' being 'watched' for is 'web-deploy'

On an agent, I issue this command:
    [pearson@ip-10-168-15-13 ~]$ consul event -name web-deploy
    Event ID: d0d4aeb8-772b-4c95-b0c6-131608351c0d
The agent 'watching' for the event now has a consul.txt file in the home directory. In this case it is in the home diectory
of the main server.

Now I want to make another agent watch for an event:
    [root@ip-10-168-15-13 pearson]# consul watch -type event -name web-deploy-agent /usr/bin/deploy-on-new-agent.sh &
    [1] 3734
    [root@ip-10-168-15-13 pearson]# ps -ef | grep consul
    root      3734 28263  0 19:01 pts/1    00:00:00 consul watch -type event -name web-deploy-agent /usr/bin/deploy-on-new-agent.sh
This new event is called 'web-deploy-agent'

I now put a new 'event' command inside the bash script for 'web-deploy,' which was the initial event. The new 'event'
added will be 'web-deploy-agent'. Now issue this command from the original server:
    [root@ip-10-168-16-98 pearson]# consul event -name web-deploy
This triggers the 'watch' for 'web-deploy' and 'web-deploy-agent' which creates a new file in the home directory of the 
original server and agent. Once a 'watch' is issued on one of the agents or servers, an 'event' with a particular attribute
will trigger the 'watch' and execute a specified command.

Now, I am adding a new 'watch' to the main server to append to the consul.txt file:
    [root@ip-10-168-16-98 pearson]# ps -ef | grep consul
    root     16680 16650  0 17:05 pts/2    00:00:30 consul agent -server -bootstrap-expect 1 -data-dir /tmp/consul -node=server-boss -bind=10.168.16.98
    root     16798 16781  0 17:36 pts/3    00:00:00 consul watch -type event -name web-deploy /usr/bin/my-deploy-handler.sh
    root     17123 16781  0 20:16 pts/3    00:00:00 consul watch -type event -name add-to-consul /usr/bin/add-to-consul.sh
    root     17130 16781  0 20:16 pts/3    00:00:00 grep consul

Once the 'add-to-consul' 'event' happens, a line will be appended to the file:
    [root@ip-10-168-16-98 pearson]# consul event -name add-to-consul
    
This is what is contained in consul.txt after running the event twice:
    This is some Consul testing
    This is appending to consul.txt in a seaprate event
    This is appending to consul.txt in a separate event