Aws-sam-cli: Cannot call API running on separate localhost port

[rhlsthrm]

I am running another API service on port 3001. When I try to call it from my Lambda local function, I get an error:

2018-01-11T21:16:09.065Z f3abec54-3c7f-1f83-ea7e-691abaf23ed5 (node:1) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejectionid: 2): Error: connect ECONNREFUSED 127.0.0.1:3001

The part of the code in question (using the Axios library):

axios.get('http://localhost:3001/hello').then(response => {
  callback(null, {
    statusCode: 200,
    body: JSON.stringify({ message: JSON.stringify(response.data) })
  })
})

It works fine if I use a publicly available endpoint, the issue is only with localhost.

[PaulMaddox]

This is due to the way Docker works.

When accessing localhost (or 127.0.0.1) from within a Lambda function running in SAM Local, you're actually accessing the docker network, not your laptop/machine.

Try using the main IP address for your local machine instead. If you're using Docker for Mac, you could also use the docker.for.mac.localhost hostname.

I WANT TO CONNECT FROM A CONTAINER TO A SERVICE ON THE HOST
The Mac has a changing IP address (or none if you have no network access). From 17.06 onwards our recommendation is to connect to the special Mac-only DNS name docker.for.mac.localhost which will resolve to the internal IP address used by the host.

source: https://docs.docker.com/docker-for-mac/networking/#use-cases-and-workarounds

[mike-tedford]

If anyone runs into this while using Docker for Windows, try replacing localhost (or 127.0.0.1) with host.docker.internal

[nilinswap]

If anyone runs into this while using Docker for Windows, try replacing localhost (or 127.0.0.1) with host.docker.internal

This works for mac too. Thanks.

[guizoxxv]

For Linux use the IP address of the docker0 interface (172.17.0.1 by default).