How can I collect custom text logs from Linux App Service file system in Azure Monitor?

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How can I collect custom text logs from Linux App Service file system in Azure Monitor?

M. Vaihinger 45

I'm trying to collect custom text logs in Azure Monitor from log files saved to the file system of a Linux App Service. But I am failing to do so. What's the best way to collect custom logs from Linux App Service? Note that I don't want to rely purely on AppServiceConsoleLogs, as I noticed that they are missing some of our logs. What I've tried so far:

Collect legacy custom text logs using Log Analytics agent: I tried to set the log collection up using the Legacy custom logs feature of Log Analytics workspace as described here: https://learn.microsoft.com/en-us/azure/azure-monitor/agents/data-sources-custom-logs. Our program continuously writes logs to text files in /wwwroot/<log_directory>/.log*. I configured this path as source for a custom log table in Log Analytics workspace. I see the custom table in Log Analytics workspace, but it is empty. Also, as of today, this feature is not available anymore in the portal, even though the docs state that it'll be available until end of 2024. Thanks in advance for your insights!

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AnuragSingh-MSFT 21,551 Moderator

@M. Vaihinger , Thank you for your question.

I understand that you are trying to collect logs from your application to Log Analytics workspace. However, I was not sure of how you have deployed the app service. I am providing information on the 2 main ways through which the application can be hosted and related steps required to collect the custom logs.

Hosted on Azure App Service - this is fully managed platform for hosting App. In this scenario you don't get access to the underlying VM and Azure maintains it for you. To collect custom logs from this type of app deployment, you can

Enable Diagnostic settings for the App Service to forward custom logs to a Log Analytics workspace.
Enable Application Insights and use ILogger based logging to send logs to AppInsights/LA worksapce directly (without enabling the diagnostic settings.)

Note that, with this kind of hosting, the Log Analytics Agent Or Azure Monitor agent do not come in picture, as they are used for collecting information from Virtual machines (which is platform managed in this case).

Hosted on VM - You can also host Application on Azure VM where you would have full control of VM. In this case you can use Azure Monitor agent (the legacy - Log Analytics Agent OR the new - Azure Monitor Agent). In this case also, you have the following options for collection of logs:

Enable Application Insights and use ILogger based logging to send logs to AppInsights/LA worksapce directly - similar to app service monitoring. The same mechanism can also be used here where the AppInsights is enabled for the application hosted on VM and custom logs can be sent to AppInsights (which uses LA workspace for storing the logs)
If there are logs which are in custom location (outside the framework based logging, for example text written to custom file path), you can use the Azure Monitor Agent to collect logs from such file. I would advise using the latest Azure Monitor Agent to collect logs from these files. For details, see Collect text logs with Azure Monitor Agent

Hope this helps.

If the answer did not help, please add more context/follow-up question for it, and we will help you out. Else, if the answer helped, please click Accept answer so that it can help others in the community looking for help on similar topics.

M. Vaihinger 45 Reputation points

2023-04-28T15:07:07.4433333+00:00
@AnuragSingh-MSFT thanks for your reply!

We're hosting the apps on Azure App Service.

I enabled diagnostic settings and all built-in App Service logs are send to a log analytics workspace. As far as I understand, sending application logs is only possible via AppServiceConsoleLogs. However I would like to rely on file logs for several reasons:

some log entries are missing in AppServiceConsoleLogs. We want to ensure, that we analyze all logs and so we'd like to store the logs as close to the application as possible and then forward them to log analytics work space

multiline application logs appear as multiple log entries in log analytics workspace if we use AppServiceConsoleLogs, which makes it more difficult to run analyses on these logs.

We also activated App Service logs to FileSystem. But the content of the ...default_docker.log is also fed from console outputs. And I think we shouldn't write to from within our application.

Is there a way to collect logs from custom log files in the app service's file system? Besides, which logging architecture do you recommend for a simple system with 3 apps (1 react, 2 Django backend apis) that will be horizontally scaled to multiple instances?

Thanks for your support!

Maybe as a sidenote. In the documentation it is unfortunately not clear which features apply to Windows Web Apps only and which are available to both Linux and Windows Web Apps.
AnuragSingh-MSFT 21,551 Reputation points Moderator

2023-05-02T07:46:54.5033333+00:00
@M. Vaihinger , thank you for sharing detailed information. There are 2 ways, that the logs can get to the LA workspace:

If you write the file to Application Logs dir - /LogFiles/Application/, by enabling the diagnostic settings for "App Service Application Logs" to log Analytics workspace, the content of this folder can sync to LA workspace. For more details, see the links below:
Log Files
Overview

Other way would be to directly use ApplicationInsights logging (irrespective of the language/framework being used). This way would not require the log files to be written to the filesystem but can be uploaded from App itself - Logging with AppInsights - Python

Hope this helps.
M. Vaihinger 45 Reputation points

2023-05-02T14:45:26.96+00:00

Thanks for your feedback!

We're currently not using Application Insights. So I'll start by trying the first solution you proposed.

Just to confirm, can I write to custom log files in the /LogFiles/Application/ directory and will the content of those custom log files be synced to LA workspace?
AnuragSingh-MSFT 21,551 Reputation points Moderator

2023-05-03T02:45:08.9366667+00:00

@M. Vaihinger , yes, once you enable diagnostic settings.

However, for monitoring applications deployed to Azure App Service, ApplicationInsights is the recommended solution. For details about enabling logs using AppInsights see - Set up Azure Monitor for your Python application

Hope this helps.

Please click "Accept Answer", if the interaction here helped so that it can help others looking for information on similar question.
Eduardo Rueda Cabañas 0 Reputation points

2023-06-18T10:29:19.6633333+00:00
Hello @AnuragSingh-MSFT ,

The App Service Logs functionality must be enabled to send this data to my LA workspace?

I ask this because I already have the diagnostic configuration "App Service Application Logs" enabled and streaming to my workspace but I do not see the log that I deposit on /LogFiles/Application/.

Theses paths were not available and I had to create it:

/root/LogFiles/Application/ (does not exist).

/home/LogFiles (exists) but does not contain an Application folder.

That is why I have manually created /home/LogFiles/Application/ with the permissions that I understand as correct nobody:nogroup and I have started to write log files in this directory with no positive results. Could you tell me what I am doing wrong?

In the case that the "App Service Application Logs" functionality needs to be enabled, what will happen to the performance of my applications? Will my resources allocated to the plan be affected laterally?

Thanks in advance.

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How can I collect custom text logs from Linux App Service file system in Azure Monitor?

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