How to use Logback to write logs to custom persistent storage

This article applies to: ✔️ Java ❌ C#

This article applies to: ✔️ Basic/Standard ✔️ Enterprise

This article shows you how to load Logback and write logs to custom persistent storage in Azure Spring Apps.

Prerequisites

• An existing storage resource bound to an Azure Spring Apps instance. If you need to bind a storage resource, see How to enable your own persistent storage in Azure Spring Apps.
• The Logback dependency included in your application. For more information on Logback, see A Guide To Logback.
• The Azure Spring Apps extension for the Azure CLI

Edit the Logback configuration to write logs into a specific path

You can set the path to where logs will be written by using the logback-spring.xml example file.

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <appender name="Console"
              class="ch.qos.logback.core.ConsoleAppender">
        <!-- please feel free to customize the log layout -->
        <layout class="ch.qos.logback.classic.PatternLayout">
            <Pattern>
                %black(%d{ISO8601}) %highlight(%-5level) [%blue(%t)] %yellow(%C{1.}): %msg%n%throwable
            </Pattern>
        </layout>
    </appender>

    <appender name="RollingFile"
              class="ch.qos.logback.core.rolling.RollingFileAppender">
        <!-- 'LOGS' here is a value to be read from the application's environment variable -->
        <file>${LOGS}/spring-boot-logger.log</file>
        <!-- please feel free to customize the log layout pattern -->
        <encoder
                class="ch.qos.logback.classic.encoder.PatternLayoutEncoder">
            <Pattern>%d %p %C{1.} [%t] %m%n</Pattern>
        </encoder>

        <rollingPolicy
                class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
            <!-- rollover daily and when the file reaches 10 MegaBytes -->
            <fileNamePattern>${LOGS}/archived/spring-boot-logger-%d{yyyy-MM-dd}.%i.log
            </fileNamePattern>
            <timeBasedFileNamingAndTriggeringPolicy
                    class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP">
                <maxFileSize>10MB</maxFileSize>
            </timeBasedFileNamingAndTriggeringPolicy>
        </rollingPolicy>
    </appender>

    <!-- LOG everything at the INFO level -->
    <root level="info">
        <appender-ref ref="RollingFile" />
        <appender-ref ref="Console" />
    </root>

    <!-- LOG "com.baeldung*" at the TRACE level -->
    <logger name="com.baeldung" level="trace" additivity="false">
        <appender-ref ref="RollingFile" />
        <appender-ref ref="Console" />
    </logger>

</configuration>

In the preceding example, there are two placeholders named {LOGS} in the path for writing the application's logs to. A value needs to be assigned to the environment variable LOGS to have the log write to both the console and your persistent storage.

Use the Azure CLI to create and deploy a new app with Logback on persistent storage

1. Use the following command to create an application in Azure Spring Apps with persistent storage enabled and the environment variable set:

   az spring app create \
        --resource-group <resource-group-name> \
        --name <app-name> \
        --service <spring-instance-name> \
        --persistent-storage <path-to-json-file> \
        --env LOGS=/byos/logs
   

   Note

   The value of the LOGS environment variable can be the same as, or a subdirectory of the mountPath.

   Here's an example of the JSON file that is passed to the --persistent-storage parameter in the create command. In this example, the same value is passed for the environment variable in the CLI command above and in the mountPath property below:

   {
       "customPersistentDisks": [
           {
               "storageName": "<Storage-Resource-Name>",
               "customPersistentDiskProperties": {
                   "type": "AzureFileVolume",
                   "shareName": "<Azure-File-Share-Name>",
                   "mountPath": "/byos/logs",
                   "readOnly": false
               }
           }
       ]
   }
   

2. Use the following command to deploy your application:

   az spring app deploy \
        --resource-group <resource-group-name> \
        --name <app-name> \
        --service <spring-instance-name> \
        --artifact-path <path-to-jar-file>
   

3. Use the following command to check your application's console log:

   az spring app logs \
        --resource-group <resource-group-name> \
        --name <app-name> \
        --service <spring-instance-name>
   

   Go to the Azure Storage Account resource you bound and find the Azure file share that was attached as persistent storage. In this example, the logs will be written to the spring-boot-logger.log file at the root of your Azure file share. All of the rotated log files will be stored in the /archived folder in your Azure file share.

4. Optionally, use the following command to update the path or persistent storage of an existing app:

   The path or persistent storage where the logs are saved can be changed at any time. The application will restart when changes are made to either environment variables or persistent storage.

   az spring app update \
        --resource-group <resource-group-name> \
        --name <app-name> \
        --service <spring-instance-name> \
        --persistent-storage <path-to-new-json-file> \
        --env LOGS=<new-path>
   

Next steps

• Structured application log for Azure Spring Apps
• Analyzing logs and metrics with diagnostic settings