Containers-roadmap: [Fargate] [How to]: Is it possible to add host entry to /etc/hosts file via Fargate 1.3.0 or 1.4.0?

[poonamgp14]

I need to add host entry to /etc/hosts file via Fargate. And, extraHosts via task-definition is not supported with awsvpc. Currently, we are using Fargate 1.3.0 and ready to upgrade to 1.4.0 if the issue can be resolved with 1.4.0.

Also, question asked here - https://github.com/aws/containers-roadmap/issues/886 suggests it is possible to do via 1.3.0 and 1.4 as well. And, I cannot seem to find either ways.

Can somebody suggest how it can be done?

[mreferre]

Hi @poonamgp14. Can you talk more about your use case and the need to add to /etc/hosts?

I'll go first: I had a situation where my app needed to connect to another service via hostname only (e.g. not via a FQDN). Since ECS service discovery (which is what powers Fargate name resolution) only works with FQDN and you can't configure /etc/resolv.conf at the task level to add a search domain I came up with a workaround to inject the domain as a variable (SEARCH_DOMAIN) and then as part of the image startup script I did:

if [ $SEARCH_DOMAIN ]; then echo "search ${SEARCH_DOMAIN}" >> /etc/resolv.conf; fi 

Could you use a similar workaround to manipulate /etc/hosts?

We are looking at how to solve this more "natively" so if you can talk more about what you are trying to achieve that would help.

Thanks.

[mreferre]

https://github.com/aws/containers-roadmap/issues/892

[lifeofguenter]

This definitely works in Fargate 1.4.0:

if ! getent hosts aws-es-proxy; then
  echo "" | tee -a /etc/hosts # add empty line as /etc/hosts on fargate does not end with one!
  echo "127.0.0.1 aws-es-proxy" | tee -a /etc/hosts
fi

(as part of your entrypoint.sh or so)

[dsalamancaMS]

This definitely works in Fargate 1.4.0:

if ! getent hosts aws-es-proxy; then
  echo "" | tee -a /etc/hosts # add empty line as /etc/hosts on fargate does not end with one!
  echo "127.0.0.1 aws-es-proxy" | tee -a /etc/hosts
fi

(as part of your entrypoint.sh or so)

This one works just fine, I just confirmed.

Also /etc/hosts is mounted as RW, so there shouldn't be any issues when writing to the file.

Which also confirms why the above works

[poonamgp14]

I have similar startup script running in fargate as mentioned below:

echo "XXX.XX.XX.XXX  $HOSTNAME_SW_NODES" >> /etc/hosts
if [ -n "$(grep $HOSTNAME_SW_NODES /etc/hosts)" ]
    then
        echo "$HOSTNAME_SW_NODES was added succesfully \n $(grep $HOSTNAME_SW_NODES /etc/hosts)";
    else
        echo "Failed to Add $HOSTNAME_SW_NODES, Try again!";

However, I still get the error

<urllib3.connection.HTTPSConnection object at 0x7fca1d205190>: Failed to establish a new connection: [Errno -2] Name or service not known

It appears to me that there could be network connectivity issue since adding host entry through startup script seems to be a valid option.

[lifeofguenter]

@poonamgp14 output your complete /etc/hosts file during runtime after your modifications so you can 💯 verify it is correct/as expected.

In my case, at least for 1.4.0, I had to add an extra line-break before adding my stuff.

[ddyzhang]

Hi @poonamgp14, do you have any other questions/requests from AWS Fargate at the moment?

Do the workarounds and suggestions posted here work for your use-case?

Thanks!