AWS metadata end point not available in CodeBuild - amazon-web-services

Question

I have a django app that has a function to determine if it is being run in an EC2 or not:
def am_i_ec2():
result = False
meta = 'http://169.254.169.254/latest/meta-data/public-ipv4'
try:
result = urlopen(meta).status == 200
except Exception:
return result
return True
This obviously works fine in my local machine. It also works on the EC2s where the pipeline will eventually make the deployment:
Python 3.6.8 (default, Mar 18 2019, 18:57:19)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-28)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from urllib.request import urlopen
>>> def am_i_ec2():
... result = False
... meta = 'http://169.254.169.254/latest/meta-data/public-ipv4'
... try:
... result = urlopen(meta).status == 200
... except Exception:
... return result
... return True
...
>>> am_i_ec2()
True
However, on the CodeBuild stage, I manually added a curl line to the buildspec and I'm getting this:
[Container] 2019/07/28 21:36:11 Running command curl http://169.254.169.254/latest/meta-data/public-ipv4
curl: (7) Couldn't connect to server
[Container] 2019/07/28 21:36:11 Command did not exit successfully curl http://169.254.169.254/latest/meta-data/public-ipv4 exit status 7
I'm assuming that all the networking pieces are working fine since prior to this implementation, the build was working fine and it does some pip installations prior to this, so it does have internet access.
What I'm I missing here?

Answer 1

As already pointed out by Subin, another SO post [1] and others [2][3], you have to change the metadata endpoint for this to work. Your build is usually not running on a plain EC2 instance but in a dockerized environment or some other type of container implemented by AWS.
Use: http://169.254.170.2$AWS_CONTAINER_CREDENTIALS_RELATIVE_URI
References
[1] https://stackoverflow.com/a/47028691/10473469
[2] https://blog.jwr.io/aws/codebuild/container/iam/role/2019/05/30/iam-role-inside-container-inside-aws-codebuild.html
[3] https://aws.amazon.com/blogs/devops/how-to-create-an-ami-builder-with-aws-codebuild-and-hashicorp-packer/ ("Create a Build Specification")