Correlation ID | Kong Docs

Looking for the plugin's configuration parameters? You can find them in the Correlation ID configuration reference doc.

The Correlation ID plugin lets you correlate requests and responses using a unique ID transmitted over an HTTP header.

How it works

When you enable this plugin, it adds a new header to all of the requests processed by Kong. This header bears the name configured in config.header_name, and a unique value is generated according to config.generator.

This header is always added in calls to your upstream services, and optionally echoed back to your clients according to the config.echo_downstream setting.

If a header with the same name is already present in the client request, the plugin honors it and does not tamper with it.

Generators

uuid

Format:

xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

This format generates a heaxadecimal UUID for each request.

uuid#counter

Format:

xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx#counter

This format generates a single UUID on a per-worker basis, and further the requests simply append a counter to the UUID after a # character. The counter value starts at 0 for each worker, and gets incremented independently of the others.

This format provides better performance, but might be harder to store or process for analyzing (due to its format and low cardinality).

tracker

Format:

ip-port-pid-connection-connection_requests-timestamp

This correlation id contains more practical implications for each request.

The following is a detailed description of the field

form parameter	description
`ip`	an address of the server that accepts a request
`port`	port of the server that accepts a request
`pid`	pid of the nginx worker process
`connection`	connection serial number
`connection_requests`	current number of requests made through a connection
`timestamp`	a floating-point number for the elapsed time in seconds (including milliseconds as the decimal part) from the epoch for the current timestamp from the nginx cached time

FAQ

Can I see my correlation IDs in my Kong logs?

You can see your correlation ID in the Nginx access log if you edit your Nginx logging parameters.

To edit your Nginx parameters, do the following:

Locate Kong Gateway’s template files and make a copy of nginx_kong.lua.
Add a log_format section on the root level of the config file which includes the $http_Kong_Request_ID variable.

In the following example, we create a new log format named customformat. It’s a copy of the default combined log format, but the last line adds $http_Kong_Request_ID, preceded by the string Kong-Request-ID=. Marking the variable this way is optional, and will make testing the feature easier. Further customize the log_format by adding or removing variables:
```
log_format customformat '$remote_addr - $remote_user [$time_local] '
              '"$request" $status $body_bytes_sent  '
              '"$http_referer" "$http_user_agent" '
              'Kong-Request-ID="$http_Kong_Request_ID"';
```
Use your custom log format for the proxy access log phase. Locate the following line:
```
access_log ${PROXY_ACCESS_LOG};
```
Modify it by adding the customformat format that we just created:
```
access_log ${{PROXY_ACCESS_LOG}} customformat;
```
Note that the file contains several access_log entries. Only modify the line that uses ${PROXY_ACCESS_LOG}.
Reload Kong:
```
kong reload
```
Tail the access log:
```
tail /usr/local/kong/logs/access.log
```
You should now see Correlation ID entries in the access log.

Learn more in Custom Nginx templates & embedding Kong.

You can also use this plugin along with one of the logging plugins, or store the ID on your backend.

Next Correlation ID Configuration