Enabling custom docker images for lambda

[bkindersleytrulioo]

based on the response to this issue: #165 (comment), I am trying to emulate a lambda based on a docker image.

my host machine is Windows, I am running Docker Desktop, and I have added

volumes:
        - //var/run/docker.sock:/var/run/docker.sock

to my docker compose file

1. with the image only locally available
   i build the image and it is available from local docker. when i configure the lambda with image uri my-image:latest, the invocation fails with error pull access denied for my-image, repository does not exist or may require 'docker login'

2. with the image in a private ECR repo
   i pushed the image to a private ecr repository
   my host machine is authenticated to this repository
   i configure the lambda with image uri XXXXXXXXXXXX.dkr.ecr.us-west-2.amazonaws.com/my-image:latest
   the invocation fails with error pull access denied, repository does not exist or may require authorization: authorization failed: no basic auth credentials

as an experiment, i tried configuring the lambda with public image uri public.ecr.aws/lambda/dotnet:8. on invocation, pulling the image succeeded (but, of course, there was no code to run so it still failed)

is there some configuration i'm missing to make this work?

[bkindersleytrulioo]

this is less pressing for me now that #256 adds support for dotnet runtime, but i am still interested to know

[bkindersleytrulioo]

suspect this is the same question as #275

[hectorvent]

Hi @bkindersleytrulioo,
Thanks for you patient.

How it works
CreateFunction with PackageType=Image always succeeds, no Docker operation happens at creation time. The image is resolved lazily on the first invocation:

1. Floci checks if the image is already present in the local Docker daemon (docker inspect)
2. If found locally → uses it directly, no pull needed
3. If not found → attempts a pull using configured credentials if they are setup

Requirements

• Docker socket must be mounted: -v /var/run/docker.sock:/var/run/docker.sock
• Image must be built with the https://docs.aws.amazon.com/lambda/latest/dg/runtimes-api.html (AWS base images like public.ecr.aws/lambda/python:3.12 include this out of the box)

Your two original scenarios

Local image (my-image:latest) — works on Linux/macOS via the shared Docker socket. On Windows Docker Desktop the /var/run/docker.sock mount can sometimes prevent the local image check from working correctly.

[hectorvent]

@bkindersleytrulioo did this work for you?

[bkindersleytrulioo]

i haven't bothered trying since there is now support for .net lambda runtime

i'm happy to close the discussion