draft-ietf-rserpool-service-00.txt   draft-ietf-rserpool-service-01.txt 
Network Working Group P. Conrad Network Working Group P. Conrad
Internet-Draft University of Delaware Internet-Draft University of Delaware
Expires: June 18, 2004 P. Lei Expires: December 10, 2004 P. Lei
Cisco Systems, Inc. Cisco Systems, Inc.
December 19, 2003 June 11, 2004
Services Provided By Reliable Server Pooling Services Provided By Reliable Server Pooling
draft-ietf-rserpool-service-00.txt draft-ietf-rserpool-service-01.txt
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved. Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract Abstract
The Reliable Server Pooling architecture (abbreviated "RSerPool", and The Reliable Server Pooling architecture (abbreviated "RSerPool", and
defined in [1]), provides a set of services and protocols for defined in [1]), provides a set of services and protocols for
building fault tolerant and highly available client/server building fault tolerant and highly available client/server
applications. This memo describes the semantics of the services that applications. This memo describes the semantics of the services that
RSerPool provides to upper layer protocols. RSerPool provides to upper layer protocols.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used In This Document . . . . . . . . . . . . . 4 2. Conventions Used In This Document . . . . . . . . . . . . . . 4
3. Example Application Scenarios . . . . . . . . . . . . . . . 4 3. Example Application Scenarios . . . . . . . . . . . . . . . . 4
3.1 Example Scenario for Failover Without RSerPool . . . . . . . 4 3.1 Example Scenario for Failover Without RSerPool . . . . . . 4
3.2 Example Scenario Using RSerPool Basic Mode . . . . . . . . . 5 3.2 Example Scenario Using RSerPool Basic Mode . . . . . . . . 5
3.3 Example Scenario Using RSerPool Enhanced Mode . . . . . . . 7 3.3 Example Scenario Using RSerPool Enhanced Mode . . . . . . 7
4. Service Primitives . . . . . . . . . . . . . . . . . . . . . 8 4. Service Primitives . . . . . . . . . . . . . . . . . . . . . . 8
4.1 Initialization . . . . . . . . . . . . . . . . . . . . . . . 9 4.1 Initialization . . . . . . . . . . . . . . . . . . . . . . 9
4.2 PE Registration Services . . . . . . . . . . . . . . . . . . 9 4.2 PE Registration Services . . . . . . . . . . . . . . . . . 9
4.3 PE Selection Services . . . . . . . . . . . . . . . . . . . 9 4.3 PE Selection Services . . . . . . . . . . . . . . . . . . 9
4.4 RSerPool Managed Data Channel . . . . . . . . . . . . . . . 10 4.4 RSerPool Managed Data Channel . . . . . . . . . . . . . . 10
4.5 Failover Services . . . . . . . . . . . . . . . . . . . . . 10 4.5 Failover Services . . . . . . . . . . . . . . . . . . . . 10
4.5.1 State Cookie Exchange . . . . . . . . . . . . . . . . . . . 11 4.5.1 State Cookie Exchange . . . . . . . . . . . . . . . . 11
4.5.2 Failover Callback Function . . . . . . . . . . . . . . . . . 11 4.5.2 Failover Callback Function . . . . . . . . . . . . . . 11
4.5.3 Business Card . . . . . . . . . . . . . . . . . . . . . . . 13 4.5.3 Business Card . . . . . . . . . . . . . . . . . . . . 13
5. Transport Mappings . . . . . . . . . . . . . . . . . . . . . 13 5. Transport Mappings . . . . . . . . . . . . . . . . . . . . . . 13
5.1 Defined Transport Mappings . . . . . . . . . . . . . . . . . 13 5.1 Defined Transport Mappings . . . . . . . . . . . . . . . . 13
5.2 Transport Mappings Requirements . . . . . . . . . . . . . . 14 5.2 Transport Mappings Requirements . . . . . . . . . . . . . 14
5.2.1 Mappings: Mandatory Requirements . . . . . . . . . . . . . . 14 5.2.1 Mappings: Mandatory Requirements . . . . . . . . . . . 14
5.2.2 Mappings: Optional Requirements . . . . . . . . . . . . . . 14 5.2.2 Mappings: Optional Requirements . . . . . . . . . . . 14
5.2.3 Mappings: Other Requirements . . . . . . . . . . . . . . . . 15 5.2.3 Mappings: Other Requirements . . . . . . . . . . . . . 15
6. Security Considerations . . . . . . . . . . . . . . . . . . 15 6. Security Considerations . . . . . . . . . . . . . . . . . . . 15
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . 15 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
References . . . . . . . . . . . . . . . . . . . . . . . . . 16 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . 17 Intellectual Property and Copyright Statements . . . . . . . . 17
1. Introduction 1. Introduction
The Reliable Server Pooling architecture is defined in [1]. The The Reliable Server Pooling architecture is defined in [1]. The
central idea of this architecture is to provide client applications central idea of this architecture is to provide client applications
("pool users") with the ability to select a server (a "pool element") ("pool users") with the ability to select a server (a "pool element")
from among a group of servers providing equivalent service (a from among a group of servers providing equivalent service (a
"pool"). The pool is accessed via an identifier called a "pool "pool"). The pool is accessed via an identifier called a "pool
handle". The RSerPool architecture supports high-availabilty and handle". The RSerPool architecture supports high-availabilty and
load balancing by enabling a pool user to identify the most load balancing by enabling a pool user to identify the most
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of a secondary server, the application invokes the service of a secondary server, the application invokes the service
primitive GETNEXTSERVER, which performs two functions in a single primitive GETNEXTSERVER, which performs two functions in a single
operation. operation.
1. First it indicates to the RSerPool layer the failure of the 1. First it indicates to the RSerPool layer the failure of the
server returned by a previous GETPRIMARYSERVER or server returned by a previous GETPRIMARYSERVER or
GETNEXTSERVER call. GETNEXTSERVER call.
2. Second, it provides the IP address of the next server that 2. Second, it provides the IP address of the next server that
should be contacted, according to the best information should be contacted, according to the best information
available to the RSerPool layer at the present time (e.g. set available to the RSerPool layer at the present time (e.g.
of available pool elements, pool element policy in effect for set of available pool elements, pool element policy in effect
the pool, etc.). for the pool, etc.).
For pool element ("server") applications where an ASAP implementation For pool element ("server") applications where an ASAP implementation
is available, two changes are required to the application source is available, two changes are required to the application source
code: code:
1. The server should invoke the REGISTER service primitive upon 1. The server should invoke the REGISTER service primitive upon
startup to add itself into the server pool using an appropriate startup to add itself into the server pool using an appropriate
pool handle. This also includes the address(es) protocol or pool handle. This also includes the address(es) protocol or
mapping id, port (if required by the mapping), and pooling mapping id, port (if required by the mapping), and pooling
policy(s). policy(s).
2. The server should invoke the DEREGISTER service primitive to 2. The server should invoke the DEREGISTER service primitive to
remove itself from the server pool when shutting down. remove itself from the server pool when shutting down.
When using these RSerPool services, RSerPool provides benefits that When using these RSerPool services, RSerPool provides benefits that
are limited (as compared to utilizing all services, described in are limited (as compared to utilizing all services, described in
Section 3.3), but nevertheless quite useful as compared to not using Section 3.3), but nevertheless quite useful as compared to not using
RSerPool at all (as in Section 3.1). First, the client user need only RSerPool at all (as in Section 3.1). First, the client user need
supply a single string, i.e. the pool handle, rather than a list of only supply a single string, i.e. the pool handle, rather than a
servers. Second, the decision as to which server is to be used can be list of servers. Second, the decision as to which server is to be
determined dynamically by the server selection mechanism (i.e. a used can be determined dynamically by the server selection mechanism
"pool policy" performed by ASAP; see [1]). Finally, when failures (i.e. a "pool policy" performed by ASAP; see [1]). Finally, when
occur, these are reported to the pool via signaling present in ASAP failures occur, these are reported to the pool via signaling present
[5]) and ENRP [4], other clients will eventually know (once this in ASAP [5]) and ENRP [4], other clients will eventually know (once
failure is confirmed by other elements of the RSerPool architecture) this failure is confirmed by other elements of the RSerPool
that this server has failed. architecture) that this server has failed.
Utilizing this subset of services is useful for: Utilizing this subset of services is useful for:
applications built over connectionless protocols such as UDP that applications built over connectionless protocols such as UDP that
cannot easily be adapted to the transport layer requirements cannot easily be adapted to the transport layer requirements
required for enhanced services (see section Section 5) required for enhanced services (see section Section 5)
applications running on systems which do not provide an applications running on systems which do not provide an
appropriate mapping layer for the desired transport protcol appropriate mapping layer for the desired transport protcol
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Additionally, if the application at PU A is aware of some Additionally, if the application at PU A is aware of some
particular PEs of pool X that would be preferred for B to contact particular PEs of pool X that would be preferred for B to contact
in the event that A becomes unreachable from B, PU A can provide in the event that A becomes unreachable from B, PU A can provide
that list to the ASAP layer, and it will be included in A's that list to the ASAP layer, and it will be included in A's
business card. (See Section 4.5.3)). business card. (See Section 4.5.3)).
Retrofitting an existing application for Enhanced Mode requires more Retrofitting an existing application for Enhanced Mode requires more
application programmer effort than retrofitting an application for application programmer effort than retrofitting an application for
Basic Mode. In particular, all use of the transport layer's Basic Mode. In particular, all use of the transport layer's
primitives (e.g. the calls to the sockets API) must be replaced by primitives (e.g. the calls to the sockets API) must be replaced by
the use of the RSerPool primitives (e.g. the RSerPool API). This can the use of the RSerPool primitives (e.g. the RSerPool API). This
be mitigated by making the RSerPool API as close to existing can be mitigated by making the RSerPool API as close to existing
transport APIs as possible. However, the benefit is that failure transport APIs as possible. However, the benefit is that failure
detection and failover is automated in this case. This automatic detection and failover is automated in this case. This automatic
failure detection takes advantage of heartbeat mechanisms that are failure detection takes advantage of heartbeat mechanisms that are
provided either in the underlying transport protocol, or in a mapping provided either in the underlying transport protocol, or in a mapping
defined on top of that protocol (see Section 4.5). defined on top of that protocol (see Section 4.5).
Provided that developers of APIs for RSerPool stay close to familiar Provided that developers of APIs for RSerPool stay close to familiar
APIs for existing transport protocols, the effort of writing a new APIs for existing transport protocols, the effort of writing a new
applications over RSerPool Enhanced Mode need not be significantly applications over RSerPool Enhanced Mode need not be significantly
different from writing the same application directly over a supported different from writing the same application directly over a supported
transport protocol or mapping. transport protocol or mapping.
4. Service Primitives 4. Service Primitives
Upper layer protocols and applications may "choose" to use these Upper layer protocols and applications may "choose" to use these
primitive services as needed. By selecting and using the appropriate primitive services as needed. By selecting and using the appropriate
set of service primitives, a range of failover scenarios may be set of service primitives, a range of failover scenarios may be
supported. These service primitives are described in the sub-sections supported. These service primitives are described in the
that follow. sub-sections that follow.
4.1 Initialization 4.1 Initialization
The INITIALIZE service is used to establish a service access point to The INITIALIZE service is used to establish a service access point to
communicate with the ASAP layer on the local host. This is the first communicate with the ASAP layer on the local host. This is the first
service accessed by either a PU or a PE. service accessed by either a PU or a PE.
4.2 PE Registration Services 4.2 PE Registration Services
Pool Elements ("server") must use the following services to add or Pool Elements ("server") must use the following services to add or
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be added to the ASAP draft, or this service should be removed from be added to the ASAP draft, or this service should be removed from
the services draft, after discussion on the list. Open question: the services draft, after discussion on the list. Open question:
does the cookie feature eliminate the need for this feature? does the cookie feature eliminate the need for this feature?
An PU that establishing a session with a PE can specify a callback An PU that establishing a session with a PE can specify a callback
function that is invoked whenever a failover has taken place. This function that is invoked whenever a failover has taken place. This
callback function is invoked immediately after the new transport callback function is invoked immediately after the new transport
layer connection/ association is established with a new server, and layer connection/ association is established with a new server, and
gives the application the opportunity to send one or more messages gives the application the opportunity to send one or more messages
that may help the server to resume any transaction or session that that may help the server to resume any transaction or session that
was in progress when the first server failed. In essence, this allows was in progress when the first server failed. In essence, this
an application designed to put the reestablishment of state into the allows an application designed to put the reestablishment of state
PU side instead of the PE side, if desired. into the PU side instead of the PE side, if desired.
This service that complements the cookie feature, in the following This service that complements the cookie feature, in the following
way: the cookie feature provides failover hooks on the PE side, where way: the cookie feature provides failover hooks on the PE side, where
the callback is a failover hook for the PU side. The on-the-wire the callback is a failover hook for the PU side. The on-the-wire
impact is that it is important that the ASAP entity should invoke the impact is that it is important that the ASAP entity should invoke the
failover callback (if any is registered) prior to resending any failover callback (if any is registered) prior to resending any
messages from previous DATA_SEND_REQUEST primitives. messages from previous DATA_SEND_REQUEST primitives.
Note that if both a state cookie from a PU and a failover callback Note that if both a state cookie from a PU and a failover callback
are present, the state cookie should be sent before the failover are present, the state cookie should be sent before the failover
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In order to support the RSerPool framework over a variety of In order to support the RSerPool framework over a variety of
transport protocols and configurations, several mappings are defined transport protocols and configurations, several mappings are defined
to provide RSerPool services over a given transport protocol. Each to provide RSerPool services over a given transport protocol. Each
mapping translates the requirements of the RSerPool framework onto mapping translates the requirements of the RSerPool framework onto
the capabilities of the transport protocol desired (e.g. SCTP, TCP, the capabilities of the transport protocol desired (e.g. SCTP, TCP,
etc.). Initially, three mappings are defined: etc.). Initially, three mappings are defined:
NO_MAPPING (0x00): With this mapping, no RserPool control channel NO_MAPPING (0x00): With this mapping, no RserPool control channel
is provided and the application specific communication between a is provided and the application specific communication between a
pool user and the pool element (e.g. data channel) is out of scope pool user and the pool element (e.g. data channel) is out of
of RSerPool. However, pool elements can register the application scope of RSerPool. However, pool elements can register the
specific communication "protocol" and "port", and thus can be application specific communication "protocol" and "port", and thus
provided to pool users. can be provided to pool users.
SCTP (0x01): SCTP transport is used for the RSerPool control SCTP (0x01): SCTP transport is used for the RSerPool control
channel. The data channel MAY be multiplexed onto the same SCTP channel. The data channel MAY be multiplexed onto the same SCTP
association, if desired. This mapping is the preferred mapping. association, if desired. This mapping is the preferred mapping.
TCP (0x02): TCP transport is used for the RSerPool control TCP (0x02): TCP transport is used for the RSerPool control
channel. The data channel MAY be multiplexed onto the same TCP channel. The data channel MAY be multiplexed onto the same TCP
connection, if desired. connection, if desired.
A particular pool element might support any combination of these A particular pool element might support any combination of these
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[Open Issue TBD: Will there be an enumeration of the various [Open Issue TBD: Will there be an enumeration of the various
transport layer mappings that must be registered with IANA?] transport layer mappings that must be registered with IANA?]
8. Acknowledgements 8. Acknowledgements
The authors wish to thank Maureen Stillman, Qiaobing Xie, Michael The authors wish to thank Maureen Stillman, Qiaobing Xie, Michael
Tuexen, Randall Stewart, and many others for their invaluable Tuexen, Randall Stewart, and many others for their invaluable
comments. comments.
References 9 References
[1] Tuexen, M. and Q. Xie, "Architecture for Reliable Server
Pooling", draft-ietf-rserpool-arch-07 (work in progress), [1] Tuexen, M., Xie, Q., Stewart, R., Shore, M. and J. Loughney,
October 2003. "Architecture for Reliable Server Pooling",
draft-ietf-rserpool-arch-07 (work in progress), October 2003.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[3] Loughney, J., "Comparison of Protocols for Reliable Server [3] Loughney, J., "Comparison of Protocols for Reliable Server
Pooling", draft-ietf-rserpool-comp-07 (work in progress), Pooling", draft-ietf-rserpool-comp-07 (work in progress),
October 2003. October 2003.
[4] Xie, Q., Stewart, R. and M. Stillman, "Enpoint Name Resolution [4] Xie, Q., Stewart, R. and M. Stillman, "Enpoint Name Resolution
Protocol (ENRP)", draft-ietf-rserpool-enrp-07 (work in Protocol (ENRP)", draft-ietf-rserpool-enrp-08 (work in
progress), October 2003. progress), June 2004.
[5] Stewart, R., Xie, Q., Stillman, M. and M. Tuexen, "Aggregate [5] Stewart, R., Xie, Q., Stillman, M. and M. Tuexen, "Aggregate
Server Access Protocol (ASAP)", draft-ietf-rserpool-asap-08 Server Access Protocol (ASAP)", draft-ietf-rserpool-asap-09
(work in progress), October 2003. (work in progress), June 2004.
[6] Conrad, P. and P. Lei, "TCP Mapping for Reliable Server Pooling [6] Conrad, P. and P. Lei, "TCP Mapping for Reliable Server Pooling
Failover Mode", draft-ietf-rserpool-tcpmapping-00 (work in Failover Mode", draft-ietf-rserpool-tcpmapping-01 (work in
progress), June 2003. progress), December 2003.
Authors' Addresses Authors' Addresses
Phillip T. Conrad Phillip T. Conrad
University of Delaware University of Delaware
Dept. of Computer and Information Sciences Dept. of Computer and Information Sciences
103 Smith Hall 103 Smith Hall
Newark, DE 19716 Newark, DE 19716
US US
Phone: +1 302 831 8622 Phone: +1 302 831 8622
EMail: conrad@acm.org EMail: conrad@acm.org
URI: http://udel.edu/~pconrad URI: http://udel.edu/~pconrad
Peter Lei Peter Lei
Cisco Systems, Inc. Cisco Systems, Inc.
8735 W Higgins Rd, Suite 300 8735 W Higgins Rd, Suite 300
Chicago, IL 60631 Chicago, IL 60631
US US
Phone: +1 847 870 7201 Phone: +1 773 695 8201
EMail: peterlei@cisco.com EMail: peterlei@cisco.com
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