How to configure hostname in ECS Fargate task definition

Question

We are migrating from ECS to Fargate. In ECS, we could set the hostname in the task definition like this:
"hostname": "%HOST_NAME%"

It fails to create with the error 'hostname is not supported on container when networkMode=awsvpc' Is there any way to set hostname ?

Answer 1

Although documentation is clear that this is not supported, there is a workaround. You can create a bootstrap_ecs.sh file and override the container ENTRYPOINT to reference this at runtime (or else add the below to your own bootstrap script). You can use this when running from ECS. Otherwise, use your standard ENTRYPOINT and COMMAND.

bootstrap_ecs.sh

#!/bin/bash

ifconfig # prints full IP info
echo "Detecting 'eth1' interface..."
DETECTED_IP=$(ifconfig -a | grep -A2 eth1 | grep inet | awk '{print $2}' | sed 's#/.*##g' | grep "\.")
if [[ -z $DETECTED_IP ]]; then
    echo "Detecting 'eth0' interface ('eth1' not found)..."
    DETECTED_IP=$(ifconfig -a | grep -A2 eth0 | grep inet | awk '{print $2}' | sed 's#/.*##g' | grep "\." | head -1)
fi
DETECTED_HOSTNAME=$(hostname)
echo -e "\n\nDETECTED_IP=$DETECTED_IP\nDETECTED_HOSTNAME=$DETECTED_HOSTNAME\n\n"
# Note: newer OS versions us `ip` instead of `ifconfig`

# Echo for debugging. You can comment/delete the 1st and 3rd lines once everything is working.
echo -e "Current file contents:\n $(cat /etc/hosts)"
echo "$DETECTED_IP $DETECTED_HOSTNAME" >> /etc/hosts
echo -e "\n\n\nUpdated file contents:\n $(cat /etc/hosts)"

CMD="$@"
$CMD