Function to stop AWS instance before changing its instance type, and starting it afterward

modify-aws-instance-type.sh

# Change AWS instance type by hostname
function modify-aws-instance-type() {
    local hostname=$1
    if [ -z $hostname ]; then
        echo "ERR: hostname not provided, usage:"
        echo "  modify-aws-instance-type HOSTNAME INSTANCE_TYPE"
        return 1
    fi
    local instance_type=$2
    if [ -z $instance_type ]; then
        echo "ERR: instance_type not provided, usage:"
        echo "  modify-aws-instance-type HOSTNAME INSTANCE_TYPE"
        return 1
    fi

    local describe_instance=$(aws ec2 describe-instances --filters "Name=tag:Name,Values=$hostname")

    local instance_id=$(echo "$describe_instance" | jq -r '.Reservations[].Instances[0].InstanceId')
    if [ -z $instance_id ]; then
        echo "ERR: InstanceId not found for $hostname"
        return 1
    fi

    echo "$hostname -> $instance_id"

    local curr_instance_type=$(echo "$describe_instance" | jq -r '.Reservations[].Instances[0].InstanceType')
    if [[ "$instance_type" == "$curr_instance_type" ]]; then
        echo "$hostname instance type is already $instance_type"
        return 0
    fi
    echo "$hostname instance_type: $curr_instance_type"

    local validate_instance_type=$(aws ec2 describe-instance-types --instance-types $instance_type | jq -r '.InstanceTypes[0].InstanceType')
    if [[ "$validate_instance_type" != "$instance_type" ]]; then
        echo "ERR: $instance_type is not a valid instance type"
        return 1
    fi

    local state=$(echo "$describe_instance" | jq -r '.Reservations[].Instances[0].State.Name')
    if [[ "$state" != "stopped" ]]; then
        echo "stopping $hostname"
        local state=$(aws ec2 stop-instances --instance-ids $instance_id | jq -r '.StoppingInstances[0].CurrentState.Name')
        while [[ "$state" != "stopped" ]]; do
            echo "waiting for $hostname / $instance_id state = 'stopped', currently $state"
            sleep 5
            local state=$(aws ec2 describe-instances --filters "Name=tag:Name,Values=$hostname" | jq -r '.Reservations[].Instances[0].State.Name')
        done
    fi

    echo "$hostname stopped. modifying instance type to $instance_type"

    if ! aws ec2 modify-instance-attribute --instance-id $instance_id --instance-type $instance_type; then
        return 1
    fi

    echo "starting $hostname"

    local state=$(aws ec2 start-instances --instance-ids $instance_id | jq -r '.StartingInstances[0].CurrentState.Name')
    echo "$hostname is in $state state"
    return 0
}