Dynamic FQDN Node DNS Resolution based on URI with Route Domains and Caching iRule
Problem this snippet solves: Following on from the code share Ephemeral Node FQDN Resolution with Route Domains - DNS Caching iRule that I posted, I have made a few modifications based on further development and comments/questions in the original share. On an incoming HTTP request, this iRule will dynamically query a DNS server (out of the appropriate route domain) defined in a pool to determine the IP address of an FQDN ephemeral node depending on the requesting URI. The IP address will be cached in a subtable so to prevent querying on every HTTP request It will also append the route domain to the node and replace the HTTP Host header. Features of this iRule * Dynamically resolves FQDN node from requesting URI * Iterates through other DNS servers in a pool if response is invalid or no response * Caches response in the session table using custom TTL * Uses cached result if present (prevents DNS lookup on each HTTP_REQUEST event) * Appends route domain to the resolved node * Replaces host header for outgoing request How to use this snippet: Add a DNS pool with appropriate health monitors, in this example the pool is called dns_pool Add the lookup datagroup, dns_lookup_dg . This defines the parameters of the DNS query. The values in the datagroup will built up an array using the key in capitals to define the array object e.g. $myArray(FQDN) Modify the values as required: FQDN: the FQDN of the node to load balance to. DNS-RD: the outbound route domain to reach the DNS servers NODE-RD: the outbound route domain to reach the node TTL: TTL value for the DNS cache in seconds ltm data-group internal dns_lookup_dg { records { /app1 { data "FQDN app1.my-domain.com|DNS-RD %10|NODE-RD %20|TTL 300|PORT 8443" } /app2 { data "FQDN app2.my-other-domain.com|DNS-RD %10|NODE-RD %20|TTL 300|PORT 8080" } default { data "FQDN default.domain.com|DNS-RD %10|NODE-RD %20|TTL 300|PORT 443" } } type string } Code : ltm data-group internal dns_lookup_dg { records { /app1 { data "FQDN app1.my-domain.com|DNS-RD %10|NODE-RD %20|TTL 300|PORT 8443" } /app2 { data "FQDN app2.my-other-domain.com|DNS-RD %10|NODE-RD %20|TTL 300|PORT 8080" } default { data "FQDN default.domain.com|DNS-RD %10|NODE-RD %20|TTL 300|PORT 443" } } type string } when CLIENT_ACCEPTED { set dnsPool "dns_pool" set dnsCache "dns_cache" set dnsDG "dns_lookup_dg" } when HTTP_REQUEST { # set datagroup values in an array if {[class match -value [HTTP::uri] "starts_with" $dnsDG]} { set dnsValues [split [string trim [class match -value [HTTP::uri] "starts_with" $dnsDG]] "| "] } else { # set to default if URI is not defined in DG set dnsValues [split [string trim [class match -value "default" "equals" $dnsDG]] "| "] } if {([info exists dnsValues]) && ($dnsValues ne "")} { if {[catch { array set dnsArray $dnsValues set fqdn $dnsArray(FQDN) set dnsRd $dnsArray(DNS-RD) set nodeRd $dnsArray(NODE-RD) set ttl $dnsArray(TTL) set port $dnsArray(PORT) } catchErr ]} { log local0. "failed to set DNS variables - error: $catchErr" event disable return } } # check if fqdn has been previously resolved and cached in the session table if {[table lookup -notouch -subtable $dnsCache $fqdn] eq ""} { log local0. "IP is not cached in the subtable - attempting to resolve IP using DNS" # initialise loop vars set flgResolvError 0 if {[active_members $dnsPool] > 0} { foreach dnsServer [active_members -list $dnsPool] { set dnsResolvIp [lindex [RESOLV::lookup @[lindex $dnsServer 0]$dnsRd -a $fqdn] 0] # verify result of dns lookup is a valid IP address if {[scan $dnsResolvIp {%d.%d.%d.%d} a b c d] == 4} { table set -subtable $dnsCache $fqdn $dnsResolvIp $ttl # clear any error flag and break out of loop set flgResolvError 0 set nodeIpRd $dnsResolvIp$nodeRd break } else { call ${partition}log local0."$dnsResolvIp is not a valid IP address, attempting to query other DNS server" set flgResolvError 1 } } } else { call ${partition}log local0."ERROR no DNS servers are availible" event disable return } #log error if query answers are invalid if {$flgResolvError} { call ${partition}log local0."ERROR unable to resolve $fqdn" unset -nocomplain dnsServer dnsResolvIp dnsResolvIp event disable return } } else { # retrieve cached IP from subtable (verification of resolved IP compelted before being commited to table) set dnsResolvIp [table lookup -notouch -subtable $dnsCache $fqdn] set nodeIpRd $dnsResolvIp$nodeRd log local0. "IP found in subtable: $dnsResolvIp with TTL: [table timeout -subtable $dnsCache -remaining $fqdn]" } # rewrite outbound host header and set node IP with RD and port HTTP::header replace Host $fqdn node $nodeIpRd $port log local0. "setting node to $nodeIpRd $port" } Tested this on version: 12.1