F5 iRules are a powerful tool set provided by F5’s BIG-IP application delivery platform. iRules allow you to directly manipulate and manage any IP application traffic. They provide a wide range of functionalities like controlling the traffic flow, inspecting in-depth packet and session information, and maintaining persistence based on customizable parameters. iRules use an event-driven scripting language that is based on TCL (Tool Command Language).
Benefits of F5 iRules:
Customization: iRules provide in-depth traffic management capabilities, allowing you to customize your traffic flow to your specific needs.
Flexibility: They are flexible enough to handle a variety of network and application issues.
Security: iRules can be used to enhance security by identifying and mitigating security threats in real-time.
Efficiency: They allow for granular control of traffic, leading to improved application performance and network efficiency.
Recommendations for using iRules:
Careful Planning: Make sure to thoroughly plan and test your iRules in a non-production environment before deploying them.
Avoid Complexity: Try to keep your iRules as simple and clear as possible. Complex iRules can cause performance issues.
Regular Review: Regularly review and update your iRules to ensure they remain effective and efficient.
The difference between iRules and “Health Monitors”:
Health monitors are a feature of F5’s BIG-IP platform that checks the availability of a server or pool of servers. The health monitor sends regular probes to the servers and based on the server’s response (or lack thereof), it determines whether the server is available to handle traffic or not.
On the other hand, iRules are scripts that you can write to manipulate and manage the application traffic. While health monitors check for availability, iRules control and manage the traffic flow.
Examples of iRules:
1. Redirecting HTTP to HTTPS for secure connections.
2. Sending specific URI requests to specific pools of servers.
3. Implementing access control by blocking or allowing traffic based on IP address.
4. Custom load balancing methods not provided natively by the F5 BIG-IP system.
5. Logging specific HTTP headers for troubleshooting.
6. Rate limiting requests to protect against DDoS attacks.
7. Rewriting HTTP headers to add, remove or modify information.
8. Inspecting and blocking specific HTTP methods like PUT or DELETE.
9. Implementing sticky sessions based on cookies or other session identifiers.
10. Blocking traffic from certain geographic locations or based on other specific criteria.
Remember, F5 iRules are powerful but they should be used judiciously. Improper use of iRules can cause performance issues and can also impact the availability of your applications. Always test your iRules thoroughly before deploying them into production.
EXAMPLES
Here are the F5 iRules configuration examples corresponding to each of the cases I mentioned:
1. Redirecting HTTP to HTTPS for secure connections:
when HTTP_REQUEST {
if { [HTTP::uri] starts_with "/secure" } {
HTTP::redirect https://[HTTP::host][HTTP::uri]
}
}
2. Sending specific URI requests to specific pools of servers:
when HTTP_REQUEST {
if { [HTTP::uri] contains "/images" } {
pool pool-images
}
else {
pool pool-general
}
}
3. Implementing access control by blocking or allowing traffic based on IP address:
when CLIENT_ACCEPTED {
if { [IP::addr [IP::client_addr] equals 10.0.0.1] } {
drop
}
}
4. Custom load balancing methods:
when HTTP_REQUEST {
pool [class match -value [HTTP::host] equals datagroup_loadbalancing]
}
5. Logging specific HTTP headers:
when HTTP_REQUEST {
log local0. "HTTP Header: [HTTP::header values]"
}
6. Rate limiting requests:
when HTTP_REQUEST {
if {[class match [IP::client_addr]/32 equals ip_limit_datagroup] > 5} {
reject
}
}
7. Rewriting HTTP headers:
when HTTP_RESPONSE {
HTTP::header replace "Server" "My Custom Server"
}
8. Inspecting and blocking specific HTTP methods:
when HTTP_REQUEST {
if { [HTTP::method] equals "PUT" } {
HTTP::respond 405 content "Method Not Allowed"
}
}
9. Implementing sticky sessions:
when HTTP_REQUEST {
persist uie [HTTP::cookie value "JSESSIONID"]
}
10. Blocking traffic from certain geographic locations:
when CLIENT_ACCEPTED {
if { [class match [IP::client_addr] equals geolocation_datagroup] equals "deny" } {
drop
}
}
Please note that these are simplified examples to provide an idea of how iRules work. Always thoroughly test iRules in a non-production environment before implementing them in a live setting. Additionally, the actual implementation of iRules can depend on many factors, including your network architecture, BIG-IP configuration, and specific use case. Always refer to F5’s official documentation or consult with an F5 expert when creating iRules.