Consul.io Leader discovery and election to invoque migration...

migration.sh

  # check if leader exist (means associated session with the )
  hasSession=$(curl -s http://localhost:8500/v1/kv/service/migration/leader | jq -r .[] | jq 'has("Session")')
  if [ -z "$hasSession" ] || [ "$hasSession" = false ]; then
    # create session
    session=$(curl -s -X PUT -d '{"Name": "migration"}' http://localhost:8500/v1/session/create | jq -r .ID)
    echo "session=$session"
    leaderValue=$(curl -s http://localhost:8500/v1/kv/service/migration/leader | jq -r .[].Value | base64 --decode)
    echo "leaderValue=$leaderValue"
    if [ -z "$leaderValue" ] || [ "$leaderValue" != "JOB_DONE" ]; then
      # try to put a lock
      noLeader=$(curl -s -X PUT -d $HOSTNAME http://localhost:8500/v1/kv/service/migration/leader?acquire=$session)
      echo "noLeader=$noLeader"
      
      leaderValue=$(curl -s http://localhost:8500/v1/kv/service/migration/leader | jq -r .[].Value | base64 --decode)
      echo "leaderValue=$leaderValue"
      
      if [ -z "$leaderValue" ] || [ "$noLeader" = true ]; then
        existingSession=$(curl -s http://localhost:8500/v1/kv/service/migration/leader | jq -r .[].Session)
        echo "existingSession=$existingSession"
        if [ "$session" = "$existingSession" ] && [ "$leaderValue" = "$HOSTNAME" ]; then
          echo "Migration..."
          sleep 1s
          # execute the migration
          
          # mark it as done (safe)
          curl -s -X PUT -d 'JOB_DONE' http://localhost:8500/v1/kv/service/migration/leader
        fi
        
      fi
      
    else
      echo "JOB already done!"
    fi
    clearSession=$(curl -s -X PUT http://localhost:8500/v1/session/destroy/$session)
    echo "Session cleared: $clearSession"
  else
    echo "Session Exist!"
    existingSession=$(curl -s http://localhost:8500/v1/kv/service/migration/leader | jq -r .[].Session)
    echo "existingSession=$existingSession"
  fi