Symfony Monolog Patterns

This project demonstrates 10 advanced logging techniques and configurations using Monolog in a modern Symfony application. It includes a set of console commands that you can run to see each logging concept in action.

Prerequisites

• PHP 8.2+
• Composer
• Symfony CLI (optional, but recommended)

Setup

1. Clone the repository:

   git clone https://github.com/mattleads/MonologPatterns.git
   cd MonologPatterns

2. Install dependencies:

   composer install

3. Set up the local SQLite database for the Messenger queue examples:

   php bin/console messenger:setup-transports

Examples

1. The "Black Box" Recorder: FingersCrossed Handler

Buffers all debug logs in memory during a process. If the process finishes successfully, the buffer is discarded. If an error occurs, the entire buffer (including the previous debug logs) is flushed to the log file.

Test Command:

# Runs successfully, debug logs are discarded
php bin/console app:test-fingers-crossed

# Triggers an error, flushing the preceding debug logs to var/log/dev.log
php bin/console app:test-fingers-crossed --fail

2. Segregated Channels: The "Payment" Log

Demonstrates routing specific logs to a dedicated file (payment.log) while excluding them from the main application log, using Monolog channels and Symfony's #[Target] attribute.

Test Command:

php bin/console app:process-payments
# Check var/log/payment.log and var/log/dev.main.log

3. Context Enrichment: The Processor

Automatically injects global context (like process ID, user ID, or request ID) into every log record without needing to pass it manually in every $logger->info() call.

Test Command:

php bin/console app:test-context
# Check var/log/dev.main.log to see the "pid" and "user" extra fields appended

4. GDPR Compliance: Sensitive Data Redaction

Uses a custom Monolog Processor to scan the log context array and automatically mask sensitive keys (like passwords or credit card numbers) before they are written to disk.

Test Command:

php bin/console app:import-users
# Check var/log/dev.main.log to see "***REDACTED***" values

5. Structured Logging: JSON Format

Outputs logs as JSON lines (ndjson), which allows log aggregators like ELK or Datadog to natively index fields like context.report_id.

Test Command:

php bin/console app:generate-report
# Check var/log/app.json

6. Spam Prevention: Deduplication Handler

Aggregates identical log records that occur rapidly (e.g., during a database outage) and prevents log spam by grouping them into a single summary.

Test Command:

php bin/console app:test-deduplication
# This fires 100 identical errors rapidly.
# Check var/log/dedup.log

7. Dynamic Log Levels (Runtime Debugging)

Simulates dynamic log level activation (typically done via an HTTP header like X-Debug-Session) using a console option.

Test Command:

# Only logs INFO level
php bin/console app:dynamic-debug

# Forces DEBUG level for this specific execution
php bin/console app:dynamic-debug --force-debug

8. Messenger Logging: Worker Context

Injects the Message Class/ID into the Monolog context specifically for long-running worker processes, making asynchronous logs traceable back to the originating message.

Test Command:

# 1. Dispatch a job to the queue
php bin/console app:dispatch-job

# 2. Run the worker to consume it
php bin/console messenger:consume async --limit=1 -vv
# Check var/log/dev.main.log for "Worker started message"

9. Excluding Specific Exceptions (e.g., 404s)

Demonstrates how to keep error logs clean by configuring Monolog to ignore specific expected exceptions or HTTP status codes.

Test Command:

php bin/console app:simulate-traffic
# The simulated 404 error is caught, but excluded from triggering the FingersCrossed error threshold

10. Notifier Bridge: ChatOps

Routes critical infrastructure failures directly to a Slack channel immediately, bypassing standard logs, using symfony/notifier bridged with Monolog.

Note: You must configure a valid SLACK_DSN in your .env file to see this send a real message to Slack.

Test Command:

php bin/console app:trigger-critical-alert