Website down - 404 Not Found error

Question

Website down - 404 Not Found error

Stephanie O'Donoghue 0

Our website (hosted on Azure) was working okay last week. Since yesterday it has been down and the URL just returns a 404 Not Found error. We have not made any changes so what could have caused this to happen?

Golla Venkata Pavani 2,330 Reputation points Microsoft External Staff Moderator

2026-03-03T09:06:01.91+00:00

Hii @Stephanie O'Donoghue,

Thank you for reaching us regarding azure‐hosted web app is suddenly returning a 404 even though you haven’t made any changes. A 404 usually means the app endpoint or files can’t be found, and it can happen for a few reasons.

Could you please provide the details via private chat to investigate the issue further.
Stephanie O'Donoghue 0 Reputation points

2026-03-03T09:09:00.2866667+00:00

Apologies for not knowing this, but how do I send a private chat message?
Golla Venkata Pavani 2,330 Reputation points Microsoft External Staff Moderator

2026-03-03T09:15:10.8166667+00:00

Hii @Stephanie O'Donoghue,

Could you please check the below screenshot to find private chat.
Golla Venkata Pavani 2,330 Reputation points Microsoft External Staff Moderator

2026-03-03T11:32:22.65+00:00
Hii @Stephanie O'Donoghue,

Thanks for sharing the details.

Based on our investigation, the web application experienced high memory utilization (≥80%) and low available swap space (≤800 MB) on the Linux App Service Plan. This led to resource exhaustion, causing the application container to become unhealthy and restart. During this period, the application was unable to respond to incoming requests, resulting in HTTP 404 errors, even though no configuration or code changes were made.

Recommended Actions:

Restart the App Service:

In the Azure Portal > Your App Service > Overview > Restart.

This often clears transient bad states. Monitor immediately after, if it comes back up, great; if 404 returns quickly, proceed to scaling.

Scale Up the App Service Plan (recommended):

Go to your App Service Plan > Scale up (change tier).

Move to the next higher tier (e.g., from B1/S1 to S2/P1v2 or higher) to give more RAM (e.g., 3.5 GB > 7 GB+).

Linux plans share resources across apps on the plan, if you have multiple apps or heavy system overhead, this buys headroom.

After scaling, restart the app again and monitor memory % (should drop significantly).

Check for Multiple Apps / Resource Contention:

If your App Service Plan hosts more than one app, even stopped ones can consume some overhead. Move production apps to dedicated plans if possible.

Reference:
https://learn.microsoft.com/en-us/azure/app-service/manage-scale-up
https://learn.microsoft.com/en-us/azure/app-service/overview-diagnostics
https://learn.microsoft.com/en-us/troubleshoot/azure/app-service/capture-memory-dumps-app-service
https://learn.microsoft.com/en-us/azure/app-service/troubleshoot-performance-degradation

Kindly let us know if the above comment helps or you need further assistance on this issue.

Please "upvote" if the information helped you. This will help us and others in the community as well.
Stephanie O'Donoghue 0 Reputation points

2026-03-04T09:16:45.95+00:00

Thank you. We tried your suggestions yesterday and the website came back up but today it is unavailable again and returning a 404 error.
Stephanie O'Donoghue 0 Reputation points

2026-03-04T17:46:49.5033333+00:00

We have now looked back and the website was fine until 1st March. As we have not made any changes, did anything change on your side on that date that could have caused the issue?
Golla Venkata Pavani 2,330 Reputation points Microsoft External Staff Moderator

2026-03-04T18:12:10.3+00:00
Hii @Stephanie O'Donoghue,

Thank you for confirming initially the issue is resolved.

I am sad to hear that after following above instructions, still you are experiencing the web app down

But when I checked from the backend, the web app still experiencing High CPU usage. Could you please confirm whether the scale up the App Service Plan to a higher tier is performed or not?

Please confirm have you restarted the web app

Could you please provide the logs via private chat to investigate the issue further by following the below path.

Azure Portal > Monitoring > Log stream

Kindly let us know if the above comment helps or you need further assistance on this issue.
Golla Venkata Pavani 2,330 Reputation points Microsoft External Staff Moderator

2026-03-09T15:47:26.4533333+00:00

Hii @Stephanie O'Donoghue,

I'm just reaching out to see if your issue has been resolved or if you've had a chance to review my previous comment?
Stephanie O'Donoghue 0 Reputation points

2026-03-10T09:30:59.37+00:00

Hi

I can confirm that we have scaled the App Service Plan to a higher tier (P1v3) and have restarted the app but the problem is still not resolved.

Which logs do you need to see? The path you have stated above does not seem to exist.
Golla Venkata Pavani 2,330 Reputation points Microsoft External Staff Moderator

2026-03-10T17:36:39.8533333+00:00
Hii @Stephanie O'Donoghue,

Thank you for the update and for confirming that the App Service Plan has been scaled to P1v3.

You can check the logs by using below steps and share logs via private chat:

Go to Microsoft Azure Portal.

Open your Azure App Service Web App.

In the left menu select Monitoring > Log stream.

You will see real-time logs from the application.

Kindly let us know if the above comment helps or you need further assistance on this issue.