Unexpected URI while testing API gateway to NLB

Question

I have a Private Link setup that points at an NLB that further has routes setup to an EC2 instance that provides my HTTP end point. I am trying to setup an API gateway to use the private link. I tried setting this up as proxy. This allows me to test an endpoint without authorization, and provide both path and query parameters. This is the log of the output I am seeing.

```
Execution log for request e114f111-f6b5-413d-9592-ec1ecb72d848
Mon Mar 07 19:38:02 UTC 2022 : Starting execution for request: e114f111-f6b5-413d-9592-ec1ecb72d848
Mon Mar 07 19:38:02 UTC 2022 : HTTP Method: GET, Resource Path: /api/falcfunnelsession/getInvestorResponse
Mon Mar 07 19:38:02 UTC 2022 : Method request path: {proxy=api/falcfunnelsession/getInvestorResponse}
Mon Mar 07 19:38:02 UTC 2022 : Method request query string: {sessionUUID=7a0e0113-05ab-4382-bed8-f91e9bc3ef3c}
Mon Mar 07 19:38:02 UTC 2022 : Method request headers: {}
Mon Mar 07 19:38:02 UTC 2022 : Method request body before transformations: 
Mon Mar 07 19:38:02 UTC 2022 : Endpoint request URI: https://funnel-backend-103-nlb-bc34d52397cf6529.elb.us-east-2.amazonaws.com?sessionUUID=7a0e0113-05ab-4382-bed8-f91e9bc3ef3c
Mon Mar 07 19:38:02 UTC 2022 : Endpoint request headers: {x-amzn-apigateway-api-id=8v1qbgdlb8, User-Agent=AmazonAPIGateway_8v1qbgdlb8, Host=funnel-backend-103-nlb-bc34d52397cf6529.elb.us-east-2.amazonaws.com}
Mon Mar 07 19:38:02 UTC 2022 : Endpoint request body after transformations: 
Mon Mar 07 19:38:02 UTC 2022 : Sending request to https://funnel-backend-103-nlb-bc34d52397cf6529.elb.us-east-2.amazonaws.com?sessionUUID=7a0e0113-05ab-4382-bed8-f91e9bc3ef3c
Mon Mar 07 19:38:07 UTC 2022 : Execution failed due to configuration error: There was an internal error while executing your request
Mon Mar 07 19:38:07 UTC 2022 : Method completed with status: 500
```

The following path and query are as expected

```
Mon Mar 07 19:38:02 UTC 2022 : HTTP Method: GET, Resource Path: /api/falcfunnelsession/getInvestorResponse
Mon Mar 07 19:38:02 UTC 2022 : Method request path: {proxy=api/falcfunnelsession/getInvestorResponse}
Mon Mar 07 19:38:02 UTC 2022 : Method request query string: {sessionUUID=7a0e0113-05ab-4382-bed8-f91e9bc3ef3c}
```
However the URI request seems to leave out the path.

```
Mon Mar 07 19:38:02 UTC 2022 : Endpoint request URI: https://funnel-backend-103-nlb-bc34d52397cf6529.elb.us-east-2.amazonaws.com?sessionUUID=7a0e0113-05ab-4382-bed8-f91e9bc3ef3c
```
Wondering is there is something I am doing wrong here. thanks!

Answer

I'm having a little trouble following where each of the log snippets is coming from.

Something to check: If you're calling API Gateway and then it is calling the PrivateLink endpoint, check to see that you've configured API Gateway to send the URI request through to PrivateLink. By the looks of it the query parameters are being sent (because `sessionUUID` is present but perhaps the URI request string isn't?

Also: Why go `API Gateway -> PrivateLink -> NLB`; why not just connect then directly `API Gateway -> NLB` as per [the documentation](https://docs.aws.amazon.com/apigateway/latest/developerguide/set-up-nlb-for-vpclink-using-console.html)?

Answer

When you integrate with a backend in a VPC you need to use a VPC Link to talk to an NLB in the VPC, as described in the tutorial. As you need to define an integration for each API endpoint, you could use the same VPC link for all of them and in each such integration you can define a different path. If you use {Proxy+} integration, which maps all the subset of the paths where it is configured to the same backend, it will be up to the backend to decide what to do based on the path which will be included in the JSON payload.

Unexpected URI while testing API gateway to NLB

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