Zope Replication Services

Replicating Mission Critical Data

The Zope Replication Service (ZRS) family of products increases the reliability and performance for all Zope enterprise clusters. ZRS provides storages that maintain redundant data storage and eliminate the storage system as a single point of failure.

Sites with high availability requirements must guard against planned and unplanned downtimes. Planned outages include system maintenance, software and operating system upgrades, and backups. Unplanned outages include system and hardware failures. ZRS reduces the downtime associated with these events by:

• replicating and distributing mission-critical data storage across distinct physical storages, including in distinct geographic locations
• providing fast, transparent failover to a standby server, and
• providing tools for managing and monitoring the standby servers.

Back-up and Maintenance

Should the primary storage fail, a secondary storage can take its place. Zope servers will transparently reconnect to the new ZRS server. Secondary servers can be taken off-line at any time to undergo repairs, backups, or system upgrades. When a secondary returns to service, it automatically resynchronizes with the primary server.

ZRS makes scheduled maintenance manageable, because primary service can be shifted to a secondary while the primary machine is being upgraded. ZRS also improves scalability since secondary servers provide additional read-only ZEO connections while maintaining their replication functions. ZEO client storages can thus be configured to connect to any available secondary, or load-balance among the available secondary ZRS servers.ZRS makes scheduled maintenance manageable, because primary service can be shifted to a secondary while the primary machine is being upgraded. ZRS also improves scalability since secondary servers can optionally provide additional read-only ZEO connections while maintaining their replication functions. ZEO client storages can thus be configured to connect to any available secondary, or load-balance among the available secondary ZRS servers.

Scalability

Adding new secondary ZRS Servers to the system is a simple process of adding the machine description to a configuration file, and starting the secondary software on the new host. A recovery process is initiated on the newly commissioned secondary storage, ensuring that it is current with respect to the primary storage.

Technical Theory of Operation

In a typical ZRS installation, the normal ZEO storage server is augmented with software that replicates transaction information at the storage API layer. (Note: ZRS does not require the use of ZEO.) A ZRS system contains a single read-write primary server and any number of read-only secondary servers. When a transaction is committed at the primary server, the transaction is replicated to all available secondary servers. If a secondary server is taken off-line, it will perform an automatic recovery process when brought back on-line. New secondaries can be added to the system at any time to improve availability.

ZRS secondary servers provide read-only access to databases. For sites that do not update content frequently, ZEO secondary servers can handle all Zope traffic. For more dynamic sites, a secondary server can provide read-only service if a failure occurs. In either case, a secondary server can be switched to primary service if the primary were to fail. Only one primary server may operate at a time.

A ZRS storage, like a ZEO server, is a wrapper which does not actually store objects on disk directly. Instead, it delegates that work to a concrete storage such as FileStorage.

Software Compatibility

• ZRS is compatible with Zope versions 2.8 and above

Pricing and Availability

Support contracts may be purchased separately. For support levels, please see Support Offerings.

For additional information, or to purchase a license, please contact sales@zope.com or call 1-540-361-1710.

Zope Corporation delivered a system that has really improved the way we manage our web content. They worked with us to customize Zope to meet our special needs to publish, given a tiered development platform and a unique network environment. We're using their Zope Replication Server (ZRS) product to ensure the timely controlled migration of data to our production servers.
- Beth Mazur, Manager of Web Development, AARP