instance_protection.sh

#!/usr/bin/env bash
while true; do
    # API call to GoCD to retrieve list of agents + status
    OUTPUT="$(curl -s "${GOCD_URL}/api/agents" -u "${GOCD_USERNAME}:${GOCD_PASSWORD}" -H 'Accept: application/vnd.go.cd.v4+json')"
    # Extract the status of the the current agent from the returned JSON using jq
    CUR_STATE="$(echo "${OUTPUT}" | jq -r "._embedded.agents[] | select(.hostname == \"${HOSTNAME}\") | .build_state")"
    if [[ "${CUR_STATE}" == "Building" ]] && ! [[ "${CUR_STATE}" == "${PREV_STATE}" ]]; then  # if the agent's state has changed from something to Building, protect the instance
            aws autoscaling set-instance-protection --region "${EC2_REGION}" --instance-ids "${INSTANCE_ID}" --auto-scaling-group-name "${ASG_NAME}" --protected-from-scale-in &
    elif [[ "${PREV_STATE}" == "Building" ]] && ! [[ "${CUR_STATE}" == "${PREV_STATE}" ]]; then  # if the agent's state has changed from Building to something else, unprotect it
            aws autoscaling set-instance-protection --region "${EC2_REGION}" --instance-ids "${INSTANCE_ID}" --auto-scaling-group-name "${ASG_NAME}" --no-protected-from-scale-in &
    fi
    sleep 5s
    PREV_STATE="${CUR_STATE}"