Learn when to use Log Search Alerts in Azure

Log search alerts in Azure Monitor are used when you need to trigger alerts based on the logs that are generated by your Azure resources, applications, or services. These alerts are useful when metric-based alerts (based on resource performance metrics) aren’t sufficient or when you need to analyze logs for more detailed information.

Here are scenarios when log search alerts are ideal:

Complex Monitoring Beyond Metrics

If your application or infrastructure generates log data that provides insights into errors, security events, or custom application behavior, log search alerts are an effective way to monitor these logs. You might need to analyze logs that contain specific strings, error messages, or patterns, which are not captured by metric alerts.

Example:

You can create an alert based on a log search query to detect specific error messages, such as "HTTP 500 Internal Server Error" from a web application’s log data.

Monitor Security and Compliance Events

Azure logs often contain important security-related data, such as failed login attempts, unauthorized access attempts, changes to security configurations, or configuration drifts. Log search alerts can be used to monitor these events in real-time to identify security threats or compliance violations.

Example:

Alert when multiple failed login attempts are detected from a specific IP address, or when an unauthorized change is made to network security rules in an Azure Security Center log.

Detect Anomalies or Patterns in Application Logs

Log search alerts are ideal when you want to monitor application behavior, detect specific events, or identify patterns, such as a sudden spike in specific error codes, warnings, or unique events logged by your application. These patterns might not necessarily correlate to metrics but could still indicate problems or important events.

Example:

Alert when an application logs more than 1000 errors in a 5-minute period or when a specific log message appears, indicating a critical application issue.

Track and Alert on Custom Logs and User Data

If you are collecting custom logs from applications, containers, or other systems, you can set up log search alerts to detect particular patterns or values in those logs. For example, custom logs that track user interactions or business-specific transactions.

Example:

You may have custom logs for tracking purchases or transactions in your e-commerce application and want to be alerted if the number of failed transactions exceeds a threshold within a certain period.

Monitor Infrastructure Events (e.g., Resource Health or VM Logs)

Log search alerts are effective for monitoring events related to the underlying infrastructure, such as virtual machine logs, network logs, or storage logs. For example, you may need to monitor specific event codes from Azure Activity Logs or VM logs.

Example:

You can set up a log search alert to monitor for specific Event IDs in Windows Event Logs (e.g., for system crashes, disk space issues, or hardware failures).

Track Operations and Changes in Resource Management

Use log search alerts to detect changes in your Azure resources, including when a resource is created, deleted, modified, or updated. These changes may impact your environment, and alerting on such changes helps you maintain better visibility and control over your resources.

Example:

Alert when a user changes a role assignment or modifies a virtual network, as logged in the Azure Activity Log.

Alert on Application Performance Issues

While metric alerts focus on the operational performance of resources, log search alerts are used for application-level monitoring. You can search for and alert on performance-related issues that are recorded in logs, such as high response times, database query failures, or memory leaks.

Example:

You can create an alert that triggers when the application logs a "High Memory Usage" warning or if there’s a significant delay in a key API endpoint response.

Correlate Multiple Logs Across Services

In large or complex environments, you may want to correlate events across different Azure services or between cloud and on-premises systems. Log search alerts allow you to run queries that span multiple log sources, helping you correlate logs from different resources.

Example:

You can correlate logs from an Azure SQL Database, an Azure Web App, and a Network Security Group to identify the root cause of a degraded application performance or security incident.

Root Cause Analysis in Post-Incident Monitoring

After an incident or outage, it’s important to perform root cause analysis. By setting up log search alerts for specific event patterns or errors, you can proactively monitor for similar issues in the future.

Example:

After resolving an issue with failed database connections, you could set up a log search alert to detect similar error messages in the future.

When NOT to Use Log Search Alerts

While log search alerts are powerful, they might not be the best choice for:

1. Simple, performance-based monitoring: For basic metrics like CPU, memory, disk, and network usage, metric alerts are more efficient.

2. Real-time performance monitoring: Metrics offer more real-time and granular monitoring, whereas log search alerts might have a slightly higher latency due to the time needed to collect, store, and query log data.

How to Set Up Log Search Alerts

To create a log search alert in Azure Monitor:

1. Go to Azure Monitor and select Logs (under Monitoring).

2. Build a query: Use Kusto Query Language (KQL) to write a query that filters the logs you want to monitor.

3. Create an alert: Once the query is ready, click on New alert rule.

4. Set the condition: Define the threshold for the alert (e.g., when the result of the query exceeds a certain number of log entries within a defined period).

5. Define the action group: Specify what actions to take (e.g., send an email, trigger a webhook, call a Logic App).

6. Review and create the alert rule.

Summary

Log search alerts are ideal for:

1. Monitoring detailed application, infrastructure, and security logs.

2. Alerting on custom patterns, error messages, and specific operational events.

3. Detecting anomalies and trends that aren’t captured by traditional metric-based alerts.

They provide an effective mechanism for detecting and responding to complex issues in your Azure environment and are highly flexible for use in sophisticated monitoring setups.