TPF TCP/IP Load Balancing

Transcription

1 6XEFRPPLWWHH TPF TCP/IP Load Balancing Mark Gambino Any references to future plans are for planning purposes only. IBM reserves the right to change those plans at its discretion. Any reliance on such a disclosure is solely at your own risk. IBM makes no commitment to provide additional information in the future.

2 Single TPF Systems (not loosely coupled)

3 Single Server Host Server application resides in only one host Client application starts a connection: If client does not know the IP address of the server Issues gethostbyname() API If local DNS does not have the information, it communicates with remote DNS servers Client sends request to the server

4 Local DNS Has Information about Host A GGUHVV $ GGUHVV $

5 1. Client X Requests IP Address of Host A from Local DNS GGUHVV $ GGUHVV $

6 2. Local DNS Returns IP Address of Host A to Client X GGUHVV $ GGUHVV $

7 3. Client X Sends Data to Host A GGUHVV $ GGUHVV $

8 Local DNS Has No Information about Host A GGUHVV $ GGUHVV

9 1. Client X Requests IP Address of Host A from Local DNS GGUHVV $ GGUHVV

10 2. Local DNS Requests IP Address of Host A from Remote DNS GGUHVV $ GGUHVV

11 3. Remote DNS Returns IP Address of Host A to Local DNS GGUHVV $ GGUHVV $

12 4. Local DNS Returns IP Address of Host A to Client X GGUHVV $ GGUHVV $

13 5. Client X Sends Data to Host A GGUHVV $ GGUHVV $

14 Single TPF Host Conclusions If a TPF host has only one IP address (or only one IP address per application): Remote clients always connect to the same one IP address in TPF Standard DNS queries work fine No load balancing software needed in the remote client, IP routers, or TPF system TCP/IP native stack allows you to have a single IP address in TPF mapped to multiple CDLC IP routers or to one OSA-Express card

15 One TPF IP Address Using Multiple CDLC IP Routers TPF x 374x 374x IP Cloud Remote Clients

16 One VIPA Using OSA-Express TPF VIPA OSA-Express OSA-Express GbE Switch GbE Switch IP Cloud Remote Clients

17 Loosely Coupled TPF Systems

18 Types of TPF IP Addresses CDLC IP address IP address of TPF for one or more CDLC IP routers Real IP address for OSA-Express Real IP address of TPF across one OSA-Express connection Static VIPA VIPA that is permanently assigned to one TPF processor in the loosely coupled complex Movable VIPA VIPA that can be moved from one TPF processor to another in the complex

19 TPF Loosely Coupled IP Address Restrictions Each TPF host needs different IP addresses to connect to standard IP routers Two TPF hosts FDQQRW have: Same CDLC IP address defined Same real IP address defined for OSA-Express Same static VIPA defined for OSA-Express A movable VIPA for OSA-Express can be defined on all TPF hosts in the complex The VIPA is active on RQHDQGRQO\RQH TPF host at any time

20 TPF Loosely Coupled with CDLC IP Routers TPFA TPFB x 374x 374x IP Cloud TPFC TPFD Remote Clients

21 TPF Loosely Coupled Using OSA-Express TPFA VIPA TPFB VIPA OSA-Express OSA-Express OSA-Express OSA-Express GbE Switch GbE Switch IP Cloud Remote Clients

22 Multiple Hosts, Standard DNS Load Balancing Server application resides in multiple hosts within a complex (cluster) One host name ("ANY" in this example) entry in DNS has multiple IP addresses (one for each host) DNS passes the list of server IP addresses back to the client in response to gethostbyname() API DNS shuffle algorithm can change the order of IP addresses in the list passed back Client node (not( the client application) selects an IP address from the list passed from DNS Most platforms select the first IP address in the list passed back from DNS

23 Server Application Resides in Hosts A, B, and C +RVW% +RVW& GGUHVV $ % & $1<

24 1. Client X Asks DNS for IP Address for Host "ANY" +RVW% +RVW& GGUHVV $ % & $1<

25 2. DNS Returns List of IP Addresses for Host "ANY" +RVW% +RVW& GGUHVV $ % & $1<

26 3. Client X Selects and Sends Data to Host A +RVW% +RVW& GGUHVV $ % & $1<

27 1. Client Y Asks DNS for IP Address for Host "ANY" +RVW% +RVW& GGUHVV $ % & $1<

28 2. DNS Returns the List of IP Addresses for Host "ANY" +RVW% +RVW& GGUHVV $ % & $1<

29 3. Client Y Selects and Sends Data to Host B +RVW% +RVW& GGUHVV $ % & $1<

30 Standard DNS Load Balancing Summary Advantages: Simple, standard DNS code No special code in client, server hosts, or IP routers Limitations: DNS entries are static DNS can return IP addresses of server hosts that are not active Hosts are not involved in the host selection: Client node and its DNS server select the host Assumes all hosts are equal capacity Does not take into account how busy the hosts are at this point in time

31 Load Balancing with DNS Server Function in the Hosts DNS server function is implemented in the host complex (where the server application resides) Make primary DNS one of the hosts that is always active Allows the server complex to select the host: Based on which hosts are active Based on how busy the hosts are right now gethostbyname() responses have a small time to life (TTL) value so that remote DNS servers do not cache the information for long (or at all if TTL is 0)

32 Local DNS Has No Information about Server Hosts +RVW% +RVW& GGUHVV

33 1. Client X Requests IP Address of Host "ANY" from Local DNS +RVW% +RVW& GGUHVV

34 2. Local DNS Asks Remote DNS for IP Address of Host "ANY" +RVW% +RVW& GGUHVV

35 3. Remote DNS Selects Host C and Returns IP address RVW% +RVW& GGUHVV

36 4. Local DNS Returns IP address to Client X +RVW% +RVW& GGUHVV

37 5.Client X Sends Data to the Selected Host +RVW% +RVW& GGUHVV

38 Host (Server) DNS Load Balancing Advantages Allows hosts to participate in the host selection process Standard DNS server is still used DNS server user exit allows the host complex to select the host for a given client request based on whatever criteria the server platform wants to use IP addresses for inactive hosts are never returned No special code is required for the client nodes, client-side DNS servers, or IP routers

39 Host (Server) DNS Load Balancing Limitations Limitations: Client information (like its IP address) is not available to the server during the host selection process Client DNS server s (or intermediate DNS server s) IP address is what gets passed to the host s DNS server Most remote DNS servers honor TTL values and do not cache information when told not to; however, some client platforms cache IP address information even though the gethostbyname() response indicated not to cache the information: These platforms use the IP address that DNS returns until that IP address no longer works Makes it difficult to rebalance the load when a new host is added to the complex

40 Front-End Box Load Balancing IP router with special software is directly connected (one hop) to the server hosts Original offering was IBM s Network Dispatcher Uses "cluster IP address" concept To the remainder of the network, the cluster IP address resides in the IP router The cluster IP address is also a loopback address in each of the hosts All input messages from remote clients are sent to the cluster IP address (and, therefore, to the IP router): Software in the IP router routes the message to the host If the packet is a connection request The IP router software selects a host Optionally, the hosts can exchange information with the IP router to customize the load balancing algorithms

41 Front-End Box Load Balancing Evolution Newer implementations allow multiple IP routers to process input messages Better scalability and availability Tables need to be kept in sync across these boxes Output messages must also be sent to these IP routers to fix some of the socket termination problems

42 Cluster IP Address Is RVW% +RVW& 5RXWHU= GGUHVV $1<

43 1. Client X Asks Its Local DNS for IP Address of Host "ANY" +RVW% +RVW& 5RXWHU= GGUHVV $1<

44 2. DNS Returns IP Address of for Host "ANY" +RVW% +RVW& 5RXWHU= GGUHVV $1<

45 3. Client X Sends a TCP SYN Message to RVW% 6<1 +RVW& 5RXWHU= GGUHVV $1<

46 4. IP Router Z Assigns This Session to Host A 6<1 +RVW% +RVW& 5RXWHU= &OLHQW6HUYHU GGUHVV $1<

47 5. Host A Responds Directly to Client X 6<1$&. +RVW% +RVW& 5RXWHU= &OLHQW6HUYHU GGUHVV $1<

48 6. Client X Sends Data, Goes Through IP Router Z +RVW% GDWD +RVW& 5RXWHU= &OLHQW6HUYHU GGUHVV $1<

49 7. IP Router Z Forwards Data to Host A GDWD +RVW% +RVW& 5RXWHU= &OLHQW6HUYHU GGUHVV $1<

50 8. Host A Sends Data Directly to Client X GDWD +RVW% +RVW& 5RXWHU= &OLHQW6HUYHU GGUHVV $1<

51 Front-End Box Load Balancing Advantages All remote clients use one IP address for the host complex Some vendors offer high-availability option Backup router takes over if primary router fails Without this, all sockets fail if IP router fails

52 Front-End Box Load Balancing Disadvantages IP routers have knowledge of sockets Every packet must go through special software in IP routers Maximum number of sessions is gated by IP routers Session information can get out of sync: Between IP routers themselves Between host and the IP routers Older implementations did not handle cases where the host unconditionally ended the socket (host sends TCP reset) If TPF takes a long dump, IP routers could clean up all sockets thinking TPF is gone TPF could IPL (which cleans up all socket knowledge in TPF), and come back before the IP routers realize TPF is gone. The IP routers still think the sockets are active.

53 Front-End Box Load Balancing Disadvantages... Information exchanged between the hosts and load balancing software in the router is not standard Different for each vendor s product Only works when the host is the server Does not work when host is the client and starts a connection using the cluster IP address Only works for TCP connections Problems with UDP because it is connectionless Problems with trace tools that use RAW sockets Remote PING and TRACEROUTE requests never make it to the host

54 Movable VIPAs VIPAs were originally designed to allow sockets to survive network failures A given VIPA always resided on the same host Static VIPA Movable VIPAs allows a VIPA to be moved from one host to another host When a host fails When a new host is added to the complex When the workload is not distributed correctly among the active hosts Sockets using a movable VIPA will fail when the VIPA is moved to another host Remote clients will reconnect using same VIPA and connect to one of the remaining hosts

55 Load Balancing Using Movable VIPAs A given client always connects to the same VIPA Assume there are 12 VIPAs in the complex Goal is to have an equal amount of the traffic for each of the 12 VIPAs (8.3% of the workload for each VIPA) Assign the appropriate amount of clients to each VIPA so that the workload is distributed equally For example, distribute by application or by partner Moving a VIPA from one host to another is infrequent Only needed when the workload is not balanced Define enough VIPAs so that you can move the desired amount of traffic Too few VIPAs prevents equal load balancing Too many VIPAs complicates network management

56 4-Way Complex, 3 Active Hosts, 12 VIPAs Defined +RVW% +RVW& 5RXWHU 5RXWHU 5RXWHU 1HWZRUN +RVW'

57 1. Client X Connects to IP 4 and Client Y Connects to IP 6 +RVW% +RVW& 5RXWHU 5RXWHU 5RXWHU 1HWZRUN +RVW'

58 2. Host D Is Activated IPs 4, 7, and 9 Are Moved to Host D +RVW% +RVW& 5RXWHU 5RXWHU 5RXWHU 1HWZRUN +RVW'

59 3. Client X Reconnects to IP 4 +RVW% +RVW& 5RXWHU 5RXWHU 5RXWHU 1HWZRUN +RVW'

60 4. Host B Fails, Its VIPAs Are Moved to Other Hosts +RVW% +RVW& 5RXWHU 5RXWHU 5RXWHU 1HWZRUN +RVW'

61 5. Client Y Reconnects to IP 6 +RVW% +RVW& 5RXWHU 5RXWHU 5RXWHU 1HWZRUN +RVW'

62 Movable VIPAs Load Balancing Advantages Each client needs to know only one IP address Client side DNS can resolve IP address of TPF Client nodes that cache IP address information are not a problem anymore Host (TPF) operators control the load balancing Granularity of how much traffic is moved can be changed by adding more VIPAs When expanding the complex, VIPAs can be moved one at a time to avoid flooding the network with reconnect requests No special code is needed for the IP routers or remote client nodes No extra overhead for any flows, even the startup flows Allows all connections to a specific host application to one host if desired (or to all hosts) For applications that are not loosely coupled capable

63 Movable VIPA Load Balancing Considerations Sockets using a VIPA are broken when that VIPA is moved from one host to another; however: Moving of VIPAs should be infrequent Remote clients can reconnect right away Sockets fail when a host fails anyway Assigning which clients to which VIPAs may take some fine tuning

64 TPF TCP/IP Load Balancing Strategies TPF plans to implement: DNS server and movable VIPAs These methods work best for long-life connections TPF does QRW plan to implement or support: Any front-end box load balancing method

65 DNS Server in TPF TPF will be a DNS server for its domain Can assign multiple host names to TPF For example, a different host name per application User exit in TPF will be invoked by the DNS server code to allow the customer to assign the IP address (and therefore the host) when a remote client starts a connection Solution is network and vendor independent Will work with CDLC connections, OSA-Express (GbE) connections, and future network technology TPF will also cache information learned from other DNS servers Improves performance when TPF is the client

66 Movable VIPAs on TPF Implement movable VIPAs across OSA-Express connections Static VIPAs (permanently assigned to one host) will still exist for connections that must go to a specific TPF host TPF operator will be able to move a VIPA from one host to another via functional message Program interface will also exist User exit will be invoked when a processor is taken out of the complex, enabling VIPAs to move from the failed host to another host

67 Rationale for Not Doing Front-End Box Balancing Requires different solution for CDLC and OSA-Express Overhead for every input message Applicable only for pure TCP server nodes: Does not work when TPF is the client Does not work well for UDP or RAW sockets Socket state information can get out of sync Host to router interface is vendor-specific Does not work in all configurations, for example: Test system with two TPF LPARs in the same CEC sharing an OSA-Express card cannot both register the same cluster IP address

68 Summary TPF s TCP/IP load balancing strategies take advantage of standard protocols (like DNS and RIP) Load balancing is centralized and controlled by the TPF system Provide maximum performance and minimum overhead Questions?