View source for F5 BIG-IP - iRules

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== Viewing iRules ==

=== Viewing All iRules ===
To display all configured iRules, use the following command:

 <nowiki>
tmsh show ltm rule</nowiki>

This command lists all iRules on the system along with their current status.

=== Viewing a Specific iRule ===
To view a specific iRule by name, use:

 <nowiki>
tmsh show ltm rule <iRule_name></nowiki>

Example:
 <nowiki>
tmsh show ltm rule myrule</nowiki>

This command will display the full content of the `myrule` iRule.

== Creating and Managing iRules ==

=== Creating a New iRule ===
To create a new iRule, use the following command:

 <nowiki>
tmsh create ltm rule <iRule_name> { <iRule_script> }</nowiki>

Example:
 <nowiki>
tmsh create ltm rule myrule { when HTTP_REQUEST { log local0. "Received HTTP request" } }</nowiki>

This creates an iRule named `myrule` that logs an entry for each HTTP request received.

=== Modifying an Existing iRule ===
To modify an existing iRule, use:

 <nowiki>
tmsh modify ltm rule <iRule_name> { <new_iRule_script> }</nowiki>

Example:
 <nowiki>
tmsh modify ltm rule myrule { when HTTP_REQUEST { log local0. "Received HTTP request with URI: [HTTP::uri]" } }</nowiki>

This modifies the `myrule` iRule to log the URI of each HTTP request.

=== Deleting an iRule ===
To delete an iRule, use:

 <nowiki>
tmsh delete ltm rule <iRule_name></nowiki>

Example:
 <nowiki>
tmsh delete ltm rule myrule</nowiki>

This deletes the `myrule` iRule from the system.

== iRule Syntax and Components ==

### Basic iRule Syntax

An iRule consists of **event blocks**, which trigger actions based on specific traffic events. The basic syntax of an iRule looks like this:

 <nowiki>
when <event> {
    <action>
}</nowiki>

Example:
 <nowiki>
when CLIENTSSL_HANDSHAKE {
    log local0. "SSL handshake initiated"
}</nowiki>

### Common Events in iRules

- **HTTP_REQUEST**: Triggered when an HTTP request is received.
- **HTTP_RESPONSE**: Triggered when an HTTP response is generated.
- **CLIENTSSL_HANDSHAKE**: Triggered during the SSL handshake.
- **TCP_REQUEST**: Triggered for TCP traffic.

### Common Actions in iRules

- **log**: Logs information to the system log.
- **reject**: Rejects the connection.
- **forward**: Forwards the traffic to the next step.
- **pool**: Directs the traffic to a specific pool or server.

### Example iRule for HTTP Request Logging

 <nowiki>
when HTTP_REQUEST {
    log local0. "Received HTTP request: [HTTP::uri]"
}</nowiki>

This iRule logs each HTTP request's URI to the system log.

== Assigning iRules to Virtual Servers ==

To assign an iRule to a virtual server, use the following command:

 <nowiki>
tmsh modify ltm virtual <vs_name> rules add { <iRule_name> }</nowiki>

Example:
 <nowiki>
tmsh modify ltm virtual my_virtual_server rules add { myrule }</nowiki>

This command adds the `myrule` iRule to the `my_virtual_server` virtual server.

=== Removing an iRule from a Virtual Server ===
To remove an iRule from a virtual server, use:

 <nowiki>
tmsh modify ltm virtual <vs_name> rules delete { <iRule_name> }</nowiki>

Example:
 <nowiki>
tmsh modify ltm virtual my_virtual_server rules delete { myrule }</nowiki>

This removes the `myrule` iRule from the `my_virtual_server` virtual server.

== Troubleshooting iRules ==

=== Viewing iRule Logs ===
To view the logs generated by iRules, use the following command:

 <nowiki>
tail -f /var/log/ltm</nowiki>

This command will display the log entries created by iRules on the system.

=== Checking iRule Syntax ===
Before deploying an iRule, it is important to ensure that there are no syntax errors. To validate the syntax of an iRule, use:

 <nowiki>
tmsh show ltm rule <iRule_name> syntax</nowiki>

Example:
 <nowiki>
tmsh show ltm rule myrule syntax</nowiki>

This command checks for syntax errors in the `myrule` iRule.

=== Debugging iRules ===
For debugging iRules, use the **log** command to print debug messages to the system log. You can enable verbose logging to track the execution flow of the iRule:

 <nowiki>
log local0. "Debugging iRule execution: [HTTP::uri]"</nowiki>

Additionally, you can use the following command to increase log verbosity:

 <nowiki>
tmsh modify /sys log-config level debug</nowiki>

This will increase the level of logging on the system, helping to debug any issues with iRule execution.

== Useful Links ==

* [F5 BIG-IP iRule Documentation](https://support.f5.com/csp/article/K19240)
* [F5 BIG-IP iRule Examples](https://techdocs.f5.com/)
* [F5 iRule Tutorials](https://community.f5.com/)
* [F5 Knowledge Base](https://support.f5.com/csp/)
* [F5 Downloads](https://downloads.f5.com/)
* [F5 iRules GitHub Repository](https://github.com/f5devcentral)
* [F5 iRules YouTube Channel](https://www.youtube.com/user/F5Networks)

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