Consul based leader election with tagging support and hooks
Consul lacks a built-in feature for leader election among registered services. This tool is designed to fill that gap. It functions by designating a leader among multiple services, marking the chosen leader with a specified tag. Additionally, it allows for the execution of a script whenever a leader election occurs.
- Install Ballot
$ git clone https://github.com/ncode/ballot
$ go build- Run consul in dev mode and register two services
$ consul agent -dev -enable-script-checks=true &
$ curl --request PUT --data @examples/consul/my-service1.json http://127.0.0.1:8500/v1/agent/service/register\?replace-existing-checks\=true
$ curl --request PUT --data @examples/consul/my-service2.json http://127.0.0.1:8500/v1/agent/service/register\?replace-existing-checks\=true- Run one instance of Ballot for each service
$ ./ballot run --config $PWD/examples/config/ballot1.yaml &
$ ./ballot run --config $PWD/examples/config/ballot2.yaml &- Open consul ui http://127.0.0.1:8500/ui/dc1/services/my_service/instances
- Play with the health checks and see the election happening and moving
$ cp /bin/ls /tmp/lalala1
$ cp /bin/ls /tmp/lalala2
$ sleep 30
$ rm /tmp/lalala1
$ sleep 10
$ cp /bin/ls /tmp/lalala1
$ rm /tmp/lalala2
$ sleep 10
$ cp /bin/ls /tmp/lalala2During the call of execOnPromote and execOnDemote a few environment variables are injected incase you need to use the and port of the service for an intended automation.
$ADDRESS # IP Address of the current service elected
$PORT # Port of the service
$SESSIONID # Current SessionID of the elected master- Write tests
- Allow to pre-define the preferred leader