Azure Blob Appender

This is a custom appender for log4j2 that outputs logs to Azure Storage Blob. There are two methods, one is to specify storage account and key directly, and the other is to use application diagnostic log of Azure App Service (WebApps).

WebApps mode

App Service has an app diagnostic logging feature, which is valid only for .NET applications and not available from Java, but it can be solved. However, it is only when the execution environment is Windows.

Enable diagnostics logging for apps - Azure App Service | Microsoft Docs

How it works

Enabling App Diagnostic Logging for App Service sets the Storage URL with SAS in the DIAGNOSTICS_AZUREBLOBCONTAINERSASURL environment variable. Azure Blob Appender will output a log to append to this blob.

The environment variables to refer to are as follows, in other words, it can be used if the following environment variables are set.

• DIAGNOSTICS_AZUREBLOBCONTAINERSASURL
• WEBSITE_SITE_NAME
• WEBSITE_INSTANCE_ID

Linux-based WebApps are not available because app diagnostic logging feature is not provided.

General mode

Directly specify a storage account or key in the configuration file.

Items to be set

The items to be set are as follows. It is necessary to specify Prefix1 / Prefix2 to output in the directory structure described later.

• Storage account
• Storage account key
• Prefix 1
• Prefix 2

BLOB directory structure

In WebApps mode, it outputs with the same structure as the diagnostic log of .NET application.

{WEBSITE_SITE_NAME}/yyyy/mm/dd/HH/{WEBSITE_INSTANCE_ID}_applicationLog.txt

The following is the general mode.

{Prefix1}/yyyy/mm/dd/HH/{Prefix2}_applicationLog.txt

Configuraion

Attribute	Type	Mean
webapps	boolean	If true, the following settings are ignored in WebApps mode. Default is false
accountName	string	Storage account name. if webapps is false, it is effective.
accountKey	string	Storage account key. if webapps is false, it is effective.
containerName	string	The name of blob container. if webapps is false, it is effective.
prefix1	string	Prefix1
prefix2	string	Prefix2

Sample configurations

In webapps mode.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="info">
    <Appenders>
        <AzureBlobAppender name="azureblob" webapps="true">
            <PatternLayout pattern="[%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n" />
        </AzureBlobAppender>
    </Appenders>
    <Loggers>
        <Root level="info">
            <AppenderRef ref="azureblob" />
        </Root>
    </Loggers>
</Configuration>

In general mode.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="info">
    <Appenders>
        <AzureBlobAppender name="azureblob" 
                           accountName="<<yourstorageaccount>>>"
                           accountKey="<<yourstorageaccountkey>>"
                           containerName="<<yourblobstoragecontainername>>"
                           prefix1="${env:COMPUTERNAME}"
                           prefix2="someprefix">
            <PatternLayout pattern="[%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n" />
        </AzureBlobAppender>
    </Appenders>
    <Loggers>
        <Root level="info">
            <AppenderRef ref="azureblob" />
        </Root>
    </Loggers>
</Configuration>

Test

Set your account and key to test/resources/azureconfig.json

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