Enabling Rolling Logs with ELMAH Azure Table Storage

ELMAH (Error Logging Modules and Handlers) is an excellent library to track application wide errors in an ASP.Net web app. It also supports several storage sinks including Azure table for storing error logs.

The nuget package Elmah.AzureTableStorage has one such implementation that stores the log in Azure table storage. The implementation creates a table Elmah in the configured storage account and pushes logs to the specific storage.

Out team too uses Elmah.AzureTableStorage for multiple web applications. But recently we had a problem with the library as the log table kept growing due to lack of a maintenance process that can trim the old errors.

As I pored over the source code of Elmah.AzureTableStorage I realized implementing a rolling log for ELMAH errors will fix our current problem and work much better in future.

I went ahead and implemented ELMAH rolling logs on top of Azure table storage using Elmah.AzureTableStorage as the base implementation. I will not dwell into the implementation as it is not very complex.

Look at my fork for the implementation details. There is a new class AzureTableStorageRollingErrorLog that can be used for rolling logs. The configuration remains similar to the original library except the reference chances to the above class in config file.

 <errorLog
type="Elmah.AzureTableStorage.AzureTableStorageRollingErrorLog,     Elmah.AzureTableStorage" 
connectionStringName="ElmahAzureTableStorage" />

Once configured correctly, an error will be simultaneously recorded in two table:

• ElmahYYYYMM (Elmah201711)
• ElmahYYYYMM+1 (Elmah201712)

The use of next month table (ELMAHYYYYMM+1) allows us to query last month data from a single table when transitioning into a new month.

With rolling logs in place, past data (tables) can be easily archived!

Another important extension to the above library is the use of compression to store the AllXml data. Azure table row has limit of 1MB, and I have seen this limit being breached in past when storing logs. With compression enable it will become a bit harder to breach the limit.

If you need rolling logs for ELMAH backed by Azure Table storage, head over to my github fork.