Need help on Understanding mentioned iRules

Hi,

First, let's know about events:

HTTP_REQUEST:

An iRule event triggered when the system fully parses the complete client HTTP request headers (that is, the method, URI, version, and all headers, not including the HTTP request body).

HTTP_RESPONSE:

An iRule event triggered when the system parses all of the response status and header lines from the server response.

Note: HTTP_RESPONSE is specific to a server response passing through the load balancer, and is not triggered for locally-generated responses (e.g. sent using the HTTP::respond command)

CLIENT_ACCEPTED:

An iRule event triggered when a client has established a connection.

Complete documentation for all commands, see:

https://clouddocs.f5.com/api/irules/

Rule #1:

# When client send a HTTP request
when HTTP_REQUEST {
    # save hostname for use in response
    #
    #Stores a variable with FQDN hostname (and port when explicit) from host header during client request.
    set fqdn_name [HTTP::host]
    #
    # e.g.
    # HTTP request header
    #
    # GET /path/page?param=value HTTP/1.1
    # Host: www.mysite.com
    # User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.97 Safari/537.36
    # Accept: */*
    #
    #
    # fqdn_name = www.mysite.com
}
 
# When server respond that HTTP request
when HTTP_RESPONSE {
    # Check if the server response is a redirection to another location
    # e.g.
    #
    # HTTP/1.1 302 Found
    # Location: /login
    # Connection: Keep-Alive
    # Content-Length: 0
    #
    #
    if { [HTTP::is_redirect] }{
        # If Location header starts with "/", means that you were implicited redirected to a resource on same FQDN and protocol.
        # e.g.
        # Location: /login (Implicit location http://www.mysite.com/login)
        # Location: http://www.mysite.com/login (Explicit location)
        #
        if { [HTTP::header Location] starts_with "/" }{
            # Rewrite Location header to redirect to https protocol and fqdn stored on variable plus location address before send response to client
            HTTP::header replace Location "https://$fqdn_name[HTTP::header Location]"
            # e.g.
            # Location: /login - rewrite to - Location: https://www.mysite.com/login
            #
        } else {
            # Else, rewrite/replace protocol http to https on that location
            HTTP::header replace Location "[string map {{http://} {https://}} [HTTP::header Location]]"
            # e.g.
            # Location: http://www.mysite.com/login - rewrite to - https://www.mysite.com/login
            # Location: https://www.mysite.com/login - nothing to match or do
        }
    }
}

Rule #2:

# When client is connected to VS
when CLIENT_ACCEPTED {
# Check that the client's IP matches a record within data group wich name is stored in the static variable: $::ins-prod-xyz_class
    if { [matchclass [IP::client_addr] equals $::ins-prod-xyz_class] } {
        # If so, do a source address translation with addresses within a snat pool
        snatpool xyz_prod_snatpool
    }
}

Rule #3:

# Set order to be first on execution
# If you have multiple rules attached in VS, it should be the first request event to run
# https://clouddocs.f5.com/api/irules/priority.html
priority 0
when HTTP_REQUEST { 
  # Drop requests when user-agent/client browser is in a blacklist stored in datagroup
  if { [class match [string tolower [HTTP::header "User-Agent"]] contains undesired_agents_class ] } {
    drop 
  }
}

Rule #4:

when HTTP_REQUEST {
    # if host is learn.x1y2z3.com, then send HTTP 301 to redirect to that location
    # HTTP 301 = Moved Permanently
    if { [string tolower [HTTP::host]] equals "learn.x1y2z3.com" } {
        HTTP::respond 301 Location "https://www.abc.com/health-learn/quote/"
    }
}

Is it clear? I hope it helps.

Regards