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Magento 2 correlation id for requests and logs

v1.4.0 2023-10-27 07:54 UTC


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Magento 2 log correlation id for PHP requests/processes and magento logs.

This is useful when debugging issues on a production site as high amounts of traffic can cause many logs to be written and identifying which logs belong to a specific failing request can sometimes be difficult.

With this you should easily be able to find all associated logs for a given web request or CLI process.

  • From a web request you can look at the X-Log-Correlation-Id header then search all your magento log files for the logs corresponding to only that request.
  • You can also find the log correlation identifier attached to New Relic transactions.


Composer install the module.

composer require ampersand/magento2-log-correlation-id

Add the additional dependency injection config necessary to boot early in the application flow

mkdir app/etc/ampersand_magento2_log_correlation
cp vendor/ampersand/magento2-log-correlation-id/dev/ampersand_magento2_log_correlation/di.xml app/etc/ampersand_magento2_log_correlation/

At this point you can make any configuration changes

Run module installation

php bin/magento setup:upgrade


rm app/etc/ampersand_magento2_log_correlation/di.xml
php bin/magento module:disable Ampersand_LogCorrelationId

How it works

Entry point

This module creates a new cache decorator (src/CacheDecorator/CorrelationIdDecorator.php).

It needs to be here so that it's constructed immediately after Magento\Framework\Cache\Frontend\Decorator\Logger which is the class responsible for instantiating Magento\Framework\App\Request\Http and the Logger triggered after.

This is the earliest point in the magento stack where we can get any existing traceId from a request header (for example cf-request-id) and have it attached to any logs produced.

This cache decorator initialises the identifier which is immutable for the remainder of the request.

Exit points

  • The correlation ID is attached to web responses as X-Log-Correlation-Id in src/HttpResponse/HeaderProvider/LogCorrelationIdHeader.php
    • REST API requests work a bit differently in Magento and attach the header using src/Plugin/AddToWebApiResponse.php
  • Monolog files have the correlation ID added into their context section under the key amp_correlation_id via src/Processor/MonologCorrelationId.php
  • Magento database logs have this identifier added by src/Plugin/AddToDatabaseLogs.php
  • New Relic has this added as a custom parameter under the key amp_correlation_id
  • CLI processes have it added as their "title" by using cli_set_process_title via Ampersand\LogCorrelationId\CacheDecorator\CorrelationIdDecorator::setCliProcessTitle
  • MySQL queries have it added as a comment at the end of the query via Ampersand\LogCorrelationId\Plugin\AddToDatabaseQueries::afterGetConnection

Example usage

Firstly you need to expose the header in your logs, this is an example for apache logs

Header always note X-Log-Correlation-Id amp_correlation_id
LogFormat "%t %U %{amp_correlation_id}n" examplelogformat
CustomLog "/path/to/var/log/httpd/access_log" examplelogformat

If you are using Nginx, that's how you can add the correlation id to the access logs

log_format examplelogformat '$time_local  $request $sent_http_x_log_correlation_id'

The above configuration would give log output like the following when viewing a page

[13/Jan/2021:11:34:37 +0000] /some-cms-page/ cid-61e04d741bf78

You could then search for all magento logs pertaining to that request

$ grep -ri 61e04d741bf78 ./var/log
./var/log/system.log:[2022-01-13 16:04:14] main.INFO: some_log_entry_61e04d7e2ed03 {"amp_correlation_id":"cid-61e04d741bf78","some":"context"} []

If the request was long-running, or had an error it may also be flagged in new relic with the custom parameter amp_correlation_id

Configuration and Customisation

Add identifier to MySQL queries

Inside app/etc/ampersand_magento2_log_correlation/di.xml you can change to disabled="false"

  <type name="Magento\Framework\App\ResourceConnection">
-     <plugin name="ampersand_log_correlation_id_db_query_plugin" disabled="true" />
+     <plugin name="ampersand_log_correlation_id_db_query_plugin" disabled="false" />

This will add the correlation identifier to all queries like SELECT store_group.* FROM store_group /* 'cid-652918943af7b811319570' */

Change the key name from amp_correlation_id

You can change the monolog/new relic key from amp_correlation_id using app/etc/ampersand_magento2_log_correlation/di.xml

<type name="Ampersand\LogCorrelationId\Service\CorrelationIdentifier">
        <argument name="identifierKey" xsi:type="string">your_key_name_here</argument>

Use existing correlation id from request header

If you want to use an upstream correlation/trace ID you can define one app/etc/ampersand_magento2_log_correlation/di.xml

<type name="Ampersand\LogCorrelationId\Service\CorrelationIdentifier">
        <argument name="headerInput" xsi:type="string">X-Your-Header-Here</argument>

If this is present on the request magento will use that value for X-Log-Correlation-Id, the monolog context, and the New Relic parameter. Otherwise magento will generate one.

For example

$ 2>&1 curl  -H 'X-Your-Header-Here: abc123' -vvv | grep "X-Log-Correlation-Id"
< X-Log-Correlation-Id: abc123
$ 2>&1 curl -vvv | grep "X-Log-Correlation-Id"
< X-Log-Correlation-Id: cid-61e4194d1bea5

Custom Loggers

By default this module hooks into all vanilla magento loggers.

However third party modules may define additional loggers to write to custom files. If you want the correlation ID added to those logs as well you will need to create a module that depends on both Ampersand_LogCorrelation_Id and the module with the custom logger, you will then have to add the log handler in di.xml like so

<type name="This\Is\Some\Logger">
        <argument name="processors" xsi:type="array">
            <item name="correlationIdProcessor" xsi:type="array">
                <item name="0" xsi:type="object">Ampersand\LogCorrelationId\Processor\MonologCorrelationId</item>
                <item name="1" xsi:type="string">addCorrelationId</item>

This module provides a command to try to help you keep track of the custom loggers in your system

$ php bin/magento ampersand:log-correlation-id:list-custom-loggers
Scanning for classes which extend Monolog\Logger
- You need to run 'composer dump-autoload --optimize' for this command to work
- Use this on your local environment to configure your di.xml
- See vendor/ampersand/magento2-log-correlation-id/