---
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title: Message Logging Policy
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---

# Message Logging Policy

> For the full documentation index, see: https://docs.mulesoft.com/llms.txt

<table><colgroup><col> <col></colgroup><tbody><tr><td><p><strong>Policy name</strong></p></td><td><p>Message Logging</p></td></tr><tr><td><p><strong>Summary</strong></p></td><td><p>Logs custom messages using information from incoming requests, responses from the backend, or information from other policies applied to the same API endpoint</p></td></tr><tr><td><p><strong>Category</strong></p></td><td><p>Troubleshooting</p></td></tr><tr><td><p><strong>First Mule version available</strong></p></td><td><p>v3.8.0</p></td></tr><tr><td><p><strong>Returned Status Codes</strong></p></td><td><p>No return codes exist for this policy</p></td></tr></tbody></table>

## Summary

The Message Logging policy logs custom messages using information from incoming requests, responses
from the backend, or information from other policies applied to the same API endpoint.

For Mule Gateway this policy works with both Apache log4j and Apache log4j2.

## Prerequisites

You must have the Anypoint Platform Organization Administrators role or have permission to create or
manage APIs.

## Configuring Policy Parameters

### Mule Gateway

When you use the UI to apply the Message Logging policy to your API, you can configure the following
parameters:

![A form to add a new logging configuration](/mulesoft/current/en-us/mule-gateway/_images/apim-message-logging-policy-ui.png)

<table><colgroup><col> <col> <col></colgroup><thead><tr><th>Parameter</th><th>Description</th><th>Required?</th></tr></thead><tbody><tr><td><p>Message</p></td><td><p>A DataWeave expression to use for extracting the message to be logged Note for Mule 4 Gateway: If the payload is used as part of the message log, do not configure the Listener as non-repeatable.</p></td><td><p>Required</p></td></tr><tr><td><p>Conditional</p></td><td><p>A DataWeave Boolean expression used to specify whether a message is to be logged</p></td><td><p>Optional</p></td></tr><tr><td><p>Category</p></td><td><p>A prefix in the log message that indicates the package and class where the log is executed.</p></td><td><p>Optional</p></td></tr><tr><td><p>Level</p></td><td><p>Defines the level of message to log: INFO, WARN, ERROR, or DEBUG</p></td><td><p>Required</p></td></tr><tr><td><p>Before Calling API</p></td><td><p>Set to cause your logging policy to log messages before the API endpoint is called, taking into account the order in which this policy is applied</p></td><td><p>Optional</p></td></tr><tr><td><p>After Calling API</p></td><td><p>Set to cause your logging policy to log messages after the API endpoint is called, taking into account the order in which this policy is applied</p></td><td><p>Optional</p></td></tr></tbody></table>

#### Example of Message Logging Policy Configured from the UI

To better understand how to use the Message Logging policy, consider a fictional retail clothier
named Les Vetments. To successfully run its e-commerce portal, Les Vetments must audit the status
code of the requests made on its website.

For example, if a customer buys or returns a product, or if the company adds or removes a product
from its catalog, the transactions must be logged. The IT manager at Les Vetments applies the
Message Logging policy to the company APIs to enable logging and viewing any data or transaction
changes without making any modifications to the code.

To log the attributes of the incoming and outgoing HTTP message, Les Vetments applies the Message
Logging policy to the API with the following UI configurations:

- **Message**: #\[attributes\]

  The attributes in the payload must be logged.

- **Conditional**: Blank

  Because Les Vetments requires all attributes, no Mule expression to filter messages is specified.

- **Category**: Blank

  No prefix is required in the log sentence.

- **Level**: Info

  All types of messages are to be logged. The Info log level also includes Warn, Error, or Debug log
  messages.

- **Before Calling API**: Checked

  All transactions that occur before the API is called are to be logged.

- **After calling API**: Checked

  All transactions that occur after the API is called are to be logged.

Following this configuration, whenever customers access the Les Vetments catalogue or add or remove
items from their carts, or when an item is added or removed from the Les Vetments catalog, logs are
generated:

```text
**********************************************************************
* Policy: message-logging-1351146-proxy                              *
* OS encoding: UTF-8, Mule encoding: UTF-8                           *
*                                                                    *
**********************************************************************
21:56:50.147     11/30/2020     Worker-0     [MuleRuntime].uber.06: [message-logging-771181-proxy].771181-message-logging.CPU_LITE @71625864     INFO
event:184152a0-3370-11eb-b732-0a8c1820c088 org.mule.extension.http.api.HttpRequestAttributes
{
   Request path=/proxy/1
   Raw request path=/proxy/1
   Method=GET
   Listener path=/proxy/*
   Local Address=/172.25.159.101:8081
   Query String=
   Relative Path=/proxy/1
   Masked Request Path=/1
   Remote Address=/18.191.37.179:21836
   Request Uri=/proxy/1
   Raw request Uri=/proxy/1
   Scheme=http
   Version=HTTP/1.1
   Headers=[
      host=logging-policy.us-e2.cloudhub.io
      x-real-ip=204.14.236.154
      accept=*/*
      user-agent=curl/7.54.0
      x-forwarded-for=204.14.236.154
      x-forwarded-port=80
      x-forwarded-proto=http
      x-sigsci-agentresponse=200
      x-sigsci-mac=7caf3820a5c07d06ef827f1565678167
   ]
   Query Parameters=[]
   URI Parameters=[]
}
21:56:50.254     11/30/2020     Worker-0     [MuleRuntime].uber.07: [logging-policy].proxy.CPU_LITE @f0ce617     INFO
event:184152a0-3370-11eb-b732-0a8c1820c088 org.mule.extension.http.api.HttpResponseAttributes
{
   Status Code=200
   Reason Phrase=OK
   Headers=[
      date=Tue, 01 Dec 2020 00:56:50 GMT
      content-type=application/json; charset=utf-8
      set-cookie=__cfduid=d8afa23a4627ebef39cbc54fea223cb231606784210; expires=Thu, 31-Dec-20 00:56:50 GMT; path=/; domain=.typicode.com; HttpOnly; SameSite=Lax
      x-powered-by=Express
      x-ratelimit-limit=1000
      x-ratelimit-remaining=999
      x-ratelimit-reset=1606784265
      vary=Origin, Accept-Encoding
      access-control-allow-credentials=true
      cache-control=max-age=43200
      pragma=no-cache
      expires=-1
      x-content-type-options=nosniff
      etag=W/"53-hfEnumeNh6YirfjyjaujcOPPT+s"
      via=1.1 vegur
      cf-cache-status=MISS
      accept-ranges=bytes
      cf-request-id=06bd666d0a0000386b7a1fc000000001
      expect-ct=max-age=604800, report-uri="https://report-uri.cloudflare.com/cdn-cgi/beacon/expect-ct"
      report-to={"endpoints":[{"url":"https:\/\/a.nel.cloudflare.com\/report?s=qUAIXoQ7qqqvFzjcwGrmK2r2PcSfDZ75jFJd0Gi0BLBUMHAcnC9wJ9I%2FEHJtk%2Bra%2FXWqkA%2F5%2FlzoWoC6YS2Lew%2BqKgjhaphHqx5WrZ0CKHMalhcM9it%2Fks0qzQGwbsRzQg%3D%3D"}],"group":"cf-nel","max_age":604800}
      nel={"report_to":"cf-nel","max_age":604800}
      cf-ray=5fa8d9c1a8c6386b-IAD
   ]
}
12:18:31.770     11/18/2020     Worker-0     agw-policy-set-deployment.01     INFO
Applied policy message-logging-1351146 version 1.0.0 to API testLoggingNew-v1-v1:16481163 (16481163) in application messagelog
```

To log headers, Les Vetments uses the following code snippet in the **Message** field:

`#[attributes.headers]`

To customize the log messages based on the event and the action performed, Les Vetments uses the
following code snippet in the **Message** field:

#\['User ' ++ authentication.clientId ++ ' performed action ' ++ attributes.method ++ ' on ' ++
attributes.requestPath ++ ' with Payload: ' ++ payload\]

#### Example of Message Logging Policy Configured in XML for Mule 4

The following flow shows an example logging policy:

```xml
<?xml version="1.0" encoding="UTF-8"?>
<mule xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xmlns="http://www.mulesoft.org/schema/mule/core"
      xmlns:http-policy="http://www.mulesoft.org/schema/mule/http-policy"
      xsi:schemaLocation="http://www.mulesoft.org/schema/mule/core
      http://www.mulesoft.org/schema/mule/core/current/mule.xsd
      http://www.mulesoft.org/schema/mule/http-policy
      http://www.mulesoft.org/schema/mule/http-policy/current/mule-http-policy.xsd">

<http-policy:proxy name="102280-message-logging">
  <http-policy:source>
   <try>
	<try>
	  <logger level="INFO" message="#[payload]"
	  category="org.mule.runtime.logging.policy-102280"/>
	    <error-handler>
	     <on-error-continue>
		<logger level="DEBUG" message="Before calling API turned into an error"
			category="org.mule.runtime.logging.policy-102280"/>
	     </on-error-continue>
	    </error-handler>
	</try>
        <http-policy:execute-next/>
          <error-handler>
	    <on-error-propagate logException="false">
	    </on-error-propagate>
          </error-handler>
  </try>
  </http-policy:source>
</http-policy:proxy>
</mule>
```

## How This Policy Works

Logging a policy consists of the following sequence:

1.  A request is sent to the API.

2.  The message is logged if the following conditions are true:

    - The level and category of the log defined in the policy are included in the logger defined in
      the configuration file.

    - Either the conditional field of the policy was not set, or was set and the condition was met.

3.  The API response is returned. Message Logging Policy does not interfere with the execution of
    any policy nor its flow.

4.  The message appears in the application log.

## About the Logging Format

A message log uses the following format:

- Omni:
  `<date> [flex-gateway-envoy][<level>] wasm log <policy-name>.default.<api-name>.default.svc main: [req: <request uuid>] [accessLog] <message>`

`policy-name`: displays the name of the policy binding:

`api-name`: displays the name of the api instance:

`request uuid`: displays a unique identifier for the request that triggered the message:

- Mule: `<date> <thread name> <level> <category>: <message>`

`date` is the message logging date and timestamp.

`thread name` is the name of the event thread in which the message appears.

`level` is the logging level or type of the message, such as INFO, WARN, ERROR, and DEBUG.

`category` typically indicates the package and class where the logging occurred. The default value
is `org.mule.runtime.logging.policy-<policy id>`.

`message`: displays the message to be logged, for example, `the payload`:

`2018-01-25 18:57:29,907 [WrapperListener_start_runner] INFO org.mule: the payload`

`2022-05-04T14:50:43.035570800Z [flex-gateway-envoy][debug] wasm log ingress-http-auth.default.ingress-http.default.svc main: [req: 61c7fdcb-8d22-4cb1-852b-0d5073f23950] [accessLog] the payload`

## Logging States During Events

Message logging occurs at specific intervals during a request flow:

- Before logging an API flow:

  ![A sequence diagram that illustrates the state before logging an API flow](/mulesoft/current/en-us/mule-gateway/_images/apim-message-logging-policy-states-1.png)

- After logging an API flow:

  ![A sequence diagram that illustrates the state after logging an API flow](/mulesoft/current/en-us/mule-gateway/_images/apim-message-logging-policy-states-2.png)

- Error handler after API flow:

  ![A sequence diagram that illustrates the state after the error handler executes](/mulesoft/current/en-us/mule-gateway/_images/apim-message-logging-policy-states-3.png)

## See Also

- [Mule Messages in Mule 4](https://docs.mulesoft.com/mule-runtime/latest/about-mule-message)