[App Service] Container start server on port 8080 but app service not starting

Question

[App Service] Container start server on port 8080 but app service not starting

Maxime Meriaux 20

Hello,

I hope you're doing well.

I'm using a Linux App Service configured to run a Docker image stored in an Azure Container Registry. Here's the situation:

The image works perfectly when run locally.
The server listens on 0.0.0.0:8080 inside the container.
A health check route is available at localhost:8080/microservice/ping.

A health check is defined in the Dockerfile as follows:

  HEALTHCHECK --interval=5s --timeout=30s --start-period=10s --retries=3 CMD [ "curl", "-f", "http://localhost:8080/microservice/ping" ]

However, the App Service fails to start properly and keeps restarting the server in a loop. Here's an excerpt from the logs:

2025-05-08T10:03:16.7922800Z $ bun dist/app.js
2025-05-08T10:03:21.0032041Z Connected to Redis store
2025-05-08T10:03:22.1863981Z Connected to SMTP mailer
2025-05-08T10:03:22.2989161Z Connected to Auth database
2025-05-08T10:03:51.2077309Z Server is running on port 8080
2025-05-08T10:11:36.7681705Z error: script "start" was terminated by signal SIGTERM (Polite quit request)
2025-05-08T10:11:53.2786286Z $ bun dist/app.js
2025-05-08T10:11:56.7066869Z Connected to Redis store
2025-05-08T10:11:57.5810270Z Connected to SMTP mailer
2025-05-08T10:11:57.6512759Z Connected to Auth database
2025-05-08T10:12:49.4807312Z Server is running on port 8080
2025-05-08T10:20:12.7414067Z error: script "start" was terminated by signal SIGTERM (Polite quit request)
2025-05-08T10:20:56.6050532Z $ bun dist/app.js
2025-05-08T10:21:00.1741820Z Connected to Redis store
2025-05-08T10:21:01.7179624Z Connected to SMTP mailer
2025-05-08T10:21:02.1266103Z Connected to Auth database
2025-05-08T10:21:33.1947359Z Server is running on port 8080
2025-05-08T10:24:45.8931738Z error: script "start" was terminated by signal SIGTERM (Polite quit request)

Do you have any idea what might be causing this issue or any suggestions for debugging further?

Prabhavathi Manchala 1,370 Reputation points Microsoft External Staff Moderator

2025-05-08T13:52:04.97+00:00
Hi Maxime Meriaux,

Your container starts fine with your app binding to port 8080 and services like Redis, SMTP, and Auth DB initializing correctly. However, Azure App Service expects the app to run on port 80, and since it's not listening on that port, Azure assumes the app is unhealthy and keeps restarting it, even though it's working properly on port 8080.

Update the App Service configuration to set the WEBSITES_PORT application setting to port 8080, so Azure knows to expect your container on that port.

In the Azure Portal, go to your App Service and navigate to Settings -> Configuration -> Application settings, and add a new setting:

Name: WEBSITES_PORT

Value: 8080, then click Save and Restart the App Service.

Azure App Service doesn't use the Dockerfile's health check. Instead, configure a custom health check path in App Service for validation.

Go to App Service -> Settings -> Health check and set the path to /microservice/ping -> Save changes.

Azure will call http://<your-container>:8080/microservice/ping, using port 8080 (set via WEBSITES_PORT), and the container will be marked as healthy.

Since your server takes about 30 seconds to start, add the WEBSITES_CONTAINER_START_TIME_LIMIT setting with a value of 600 or higher to allow more startup time (default is 230 seconds).

Check that the Startup command in your App Service configuration points to the correct entry point of your application to ensure it starts properly.

https://learn.microsoft.com/en-us/azure/app-service/configure-custom-container?pivots=container-linux&tabs=debian#configure-environment-variables

https://learn.microsoft.com/en-us/azure/app-service/configure-common?tabs=portal#configure-app-settings
Prabhavathi Manchala 1,370 Reputation points Microsoft External Staff Moderator

2025-05-09T06:26:08.51+00:00

Hi Maxime Meriaux,

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Prabhavathi Manchala 1,370 Reputation points Microsoft External Staff Moderator

2025-05-12T02:28:34.1266667+00:00

Hi Maxime Meriaux,

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Sampath 3,250 Reputation points Microsoft External Staff Moderator

2025-05-12T04:20:26.34+00:00
Hello @Maxime Meriaux,

Your container is listening on port 8080, but Azure App Service expects the app to respond on port 80 unless explicitly told otherwise.

Additionally:

App Service ignores the Dockerfile HEALTHCHECK instruction — it only respects the health check configured in the Azure Portal.

If a health check fails or no response is detected on the expected port, Azure assumes the container is unhealthy and kills it.

Your app may also have a relatively slow startup (30+ seconds), which might not meet default timeout expectations.

Below are steps to Fix above error

Set an application setting so Azure knows the app listens on port 8080:

Go to Azure Portal > your App Service > Environment variables.

Add:
Name: WEBSITES_PORT Value: 8080

Save and restart the app.

Since Azure ignores the Docker HEALTHCHECK, do this instead:

Go to App Service > Settings > Health check.

Set the path to:
/microservice/ping

Azure will send requests to http://<your-container>:8080/microservice/ping.

Ensure your server handles this path and returns a 2xx status code.

If your app initializes slowly (e.g., due to connecting to Redis, SMTP, DB):

Go to App Service > Environment variables.

Add:
Name: WEBSITES_CONTAINER_START_TIME_LIMIT Value: 600

This gives your app up to 10 minutes to start before it's killed.Ensure your startup command is correctly configured:

If your container doesn’t start with CMD or ENTRYPOINT in the Dockerfile, or if you’re using a custom script, make sure it is explicitly declared in the App Service settings.

In App Service > Environment variables, confirm that the Startup (Linux only) is either blank (uses default Docker CMD), or set to something like:
bun dist/app.js

Ensure your container exposes port 8080 in the Dockerfile:

EXPOSE 8080

Although not strictly required by Azure, it helps during local debugging and clarifies intent.

Use Kudu: In App Service → Advanced Tools (Kudu) → Debug Console, you can inspect the environment and logs.

Enable diagnostics logs:

Go to Monitoring > App Service logs.

Enable Container logging and App Service logs.

Use curl or wget inside the container (via SSH or Kudu) to verify /microservice/ping is working.

Let me know in the comments if the steps I provided were helpful.
Sampath 3,250 Reputation points Microsoft External Staff Moderator

2025-05-13T07:20:46.8066667+00:00

Hi Maxime Meriaux, Just checking to see if you have seen the above messages.
Sampath 3,250 Reputation points Microsoft External Staff Moderator

2025-05-14T06:22:31.4533333+00:00

Hi @ Maxime Meriaux, We still have not heard back from you. Just checking in to see if the provided comment helped. If you have any further queries, do let us know.
Maxime Meriaux 20 Reputation points

2025-05-14T14:23:03.35+00:00

Hello everyone,

I hope you're all doing well.

I'm truly sorry for my late response, and I sincerely thank you for your feedback.

In the end, I found the issue, which turned out to be quite subtle. It wasn't related to the App Service configuration, the Dockerfile, or even the server setup itself. The server was indeed listening on port 8080, and Azure was correctly using that port.

The problem occurred after I upgraded to Elysia 1.3.0 and integrated the Elysia CORS plugin. That plugin was returning an empty response, as mentioned in this issue: https://github.com/elysiajs/elysia-cors/issues/64.

To work around it, I simply removed the CORS plugin and decided to handle CORS through the App Service instead. Note that this issue was fixed in version 1.3.1 of Elysia.

Again, sorry for the late reply :c
Sampath 3,250 Reputation points Microsoft External Staff Moderator

2025-05-14T14:31:44.01+00:00

Hello @Maxime Meriaux , Thank you for confirming that the issue is resolved. To close the question, we need to post your answer, and you need to accept and click yes. Please allow me to post the answer as part of the process. Let me know your thoughts. Thank you.
Maxime Meriaux 20 Reputation points

2025-05-14T14:42:42.74+00:00

yes I accept!

Accepted answer

0 additional answers

Your answer

Prabhavathi Manchala 1,370 Reputation points Microsoft External Staff Moderator

2025-05-08T13:52:04.97+00:00

Hi Maxime Meriaux,

Your container starts fine with your app binding to port 8080 and services like Redis, SMTP, and Auth DB initializing correctly. However, Azure App Service expects the app to run on port 80, and since it's not listening on that port, Azure assumes the app is unhealthy and keeps restarting it, even though it's working properly on port 8080.

Update the App Service configuration to set the WEBSITES_PORT application setting to port 8080, so Azure knows to expect your container on that port.

In the Azure Portal, go to your App Service and navigate to Settings -> Configuration -> Application settings, and add a new setting:

Name: WEBSITES_PORT

Value: 8080, then click Save and Restart the App Service.

Azure App Service doesn't use the Dockerfile's health check. Instead, configure a custom health check path in App Service for validation.

Go to App Service -> Settings -> Health check and set the path to /microservice/ping -> Save changes.

Azure will call http://<your-container>:8080/microservice/ping, using port 8080 (set via WEBSITES_PORT), and the container will be marked as healthy.

Since your server takes about 30 seconds to start, add the WEBSITES_CONTAINER_START_TIME_LIMIT setting with a value of 600 or higher to allow more startup time (default is 230 seconds).

Check that the Startup command in your App Service configuration points to the correct entry point of your application to ensure it starts properly.

https://learn.microsoft.com/en-us/azure/app-service/configure-custom-container?pivots=container-linux&tabs=debian#configure-environment-variables

https://learn.microsoft.com/en-us/azure/app-service/configure-common?tabs=portal#configure-app-settings
Prabhavathi Manchala 1,370 Reputation points Microsoft External Staff Moderator

2025-05-09T06:26:08.51+00:00

Hi Maxime Meriaux,

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Prabhavathi Manchala 1,370 Reputation points Microsoft External Staff Moderator

2025-05-12T02:28:34.1266667+00:00

Hi Maxime Meriaux,

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Sampath 3,250 Reputation points Microsoft External Staff Moderator

2025-05-13T07:20:46.8066667+00:00

Hi Maxime Meriaux, Just checking to see if you have seen the above messages.
Sampath 3,250 Reputation points Microsoft External Staff Moderator

2025-05-14T06:22:31.4533333+00:00

Hi @ Maxime Meriaux, We still have not heard back from you. Just checking in to see if the provided comment helped. If you have any further queries, do let us know.
Maxime Meriaux 20 Reputation points

2025-05-14T14:23:03.35+00:00

Hello everyone,

I hope you're all doing well.

I'm truly sorry for my late response, and I sincerely thank you for your feedback.

In the end, I found the issue, which turned out to be quite subtle. It wasn't related to the App Service configuration, the Dockerfile, or even the server setup itself. The server was indeed listening on port 8080, and Azure was correctly using that port.

The problem occurred after I upgraded to Elysia 1.3.0 and integrated the Elysia CORS plugin. That plugin was returning an empty response, as mentioned in this issue: https://github.com/elysiajs/elysia-cors/issues/64.

To work around it, I simply removed the CORS plugin and decided to handle CORS through the App Service instead. Note that this issue was fixed in version 1.3.1 of Elysia.

Again, sorry for the late reply :c
Sampath 3,250 Reputation points Microsoft External Staff Moderator

2025-05-14T14:31:44.01+00:00

Hello @Maxime Meriaux , Thank you for confirming that the issue is resolved. To close the question, we need to post your answer, and you need to accept and click yes. Please allow me to post the answer as part of the process. Let me know your thoughts. Thank you.
Maxime Meriaux 20 Reputation points

2025-05-14T14:42:42.74+00:00

yes I accept!

Answer 1

Hello @Maxime Meriaux

Thank you for describing the issue so clearly. I'm glad to hear the problem has resolved and I appreciate your follow-up note. Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others", I'm reposting your solution here so that you can accept the answer.

Solution:

The issue was not related to the App Service configuration, Dockerfile, or the server setup. The container was correctly listening on port 8080, and Azure was properly configured to expect it.

The actual root cause was introduced after upgrading to Elysia 1.3.0 and integrating the Elysia CORS plugin. This plugin was returning an empty response, which caused Azure's health check to fail, triggering container restarts.

As a workaround, the CORS plugin was removed, and CORS was handled directly through the App Service configuration instead. This resolved the issue. Note that this bug has been fixed in Elysia version 1.3.1.

Please click Accept Answer and kindly click Yes so others experiencing a similar issue can benefit as well.

Maxime Meriaux 20 Reputation points

2025-05-14T15:15:55.4566667+00:00

Thanks youuuuu

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[App Service] Container start server on port 8080 but app service not starting

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