DNS resolution failure from App Runner

Question

Any time my application tries to resolve a domain from within App Runner, it fails. For example, the Auth0 client fails with the following error:

`requests.exceptions.ConnectionError: HTTPSConnectionPool(host=’.us.auth0.com’, port=443): Max retries exceeded with url: /.well-known/jwks.json (Caused by NewConnectionError(’: Failed to establish a new connection: [Errno -3] Temporary failure in name resolution’))
12-27-2021 03:35:30 PM         raise ConnectionError(e, request=request)`

I was experiencing the same issue calling another service running in App Runner. I don't see any VPC settings to configure. It sounds similar to the issue here: https://repost.aws/questions/QUnm9sWqVHTyKYX_UOKnpmHg/app-runner-and-rds.

Thanks!

Answer

That issue is more about connecting to a private entity in a VPC (which is not possible - today- given that an App Runner service does not connect to a VPC). You should be able to resolve any public DNS name however. I am wondering if the FQDN you are using is malformed in some way? Can you test something really simple like curling/getting www.google.com or anything as basic in order to validate that public name resolution inside the service works?

[UPDATE]: I built this super simple/stupid application to prove an app deployed to App Runner can resolve and connect to the Internet. You can deploy it to App Runner and see how it can connect to a public website.

[UPDATE]: I built [this super simple/stupid application](https://github.com/mreferre/flask-get-url) to prove an app deployed to App Runner can resolve and connect to the Internet. You can deploy it to App Runner and see how it can connect to a public website.

Answer

We experienced the same issue, intermittent DNS lookup failures of an RDS hostname from an App Runner python microservice. For us, switching the resolver implementation to ares (GEVENT_RESOLVER="ares" environment variable) fixed these issues.

Answer

We have a similar issue with a dockerized app on AppRunner - related to DNS resolution (`Temporary failure in name resolution` => `EAI_AGAIN` error):
```
FetchError: request to https://via.placeholder.com/1000x640 failed, reason: getaddrinfo EAI_AGAIN via.placeholder.com
```

It only happens after a new deployment (new docker image to fetch) to AppRunner. After a pause/resume of the app the issue is gone. No issues when resolving AWS internal services though.
Luckily we won't use placeholder images in prod (and have no other calls to the outside).

**Update**:
In my case it seems related to `alpine` as base image (more details -> https://github.com/nodejs/docker-node/issues/1030). After switching from `node:16-alpine` to `node:16-slim`, the issue has gone.

Answer

I've tried hardcoding *google.com* and got the same error. This isn't intermittent for me - I'm getting 100% failure. I'll see if changing the resolver works, thanks!

DNS resolution failure from App Runner

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