All LifeKeeper configurations share these common components:
- Server groups. The basis for the fault resilience provided by LifeKeeper is the grouping of two or more servers into a cluster. The servers can be any supported platform running a supported distribution of Linux. LifeKeeper gives you the flexibility to configure servers in multiple overlapping groups, but, for any given recoverable resource, the critical factor is the linking of a group of servers with defined roles or priorities for that resource. The priority of a server for a given resource is used to determine which server will recover that resource should there be a failure on the server where it is currently running. The highest possible priority value is one (1). The server with the highest priority value (normally 1) for a given resource is typically referred to as the primary server for that resource; any other servers are defined as backup servers for that resource.
- Communications paths. The LifeKeeper heartbeat, a periodic message between servers in a LifeKeeper cluster, is a key fault detection facility. All servers within the cluster require redundant heartbeat communications paths (or, comm paths) to avoid system panics due to simple communications failures. Two separate LAN-based (TCP) comm paths using dual independent subnets are recommended (at least one of these should be configured as a private network); however, using a combination of TCP and TTY comm paths is supported. A TCP comm path can also be used for other system communications. Also in a cloud environment, the internal configuration of the network is not open to the public, so it is difficult to physically prepare two LAN lines with different routes. Since it is expected that the physical network is basically redundant on the cloud side, operational reliability can be ensured even if there is only one communication path.
Note: A TTY comm path is used by LifeKeeper only for detecting whether other servers in the cluster are alive. The LifeKeeper GUI uses TCP/IP for communicating status information about protected resources; if there are two TCP comm paths configured, LifeKeeper uses the comm path on the public network for communicating resource status. Therefore if the network used by the LifeKeeper GUI is down, the GUI will show hierarchies on other servers in an UNKNOWN state, even if the TTY (or other TCP) comm path is operational.
- Shared data resources. In shared storage configurations, servers in the LifeKeeper cluster share access to the same set of disks. In the case of a failure of the primary server, LifeKeeper automatically manages the unlocking of the disks from the failed server and the locking of the disks to the next available back-up server.
- Shared communication. LifeKeeper can automatically manage switching of communications resources, such as TCP/IP addresses, allowing users to connect to the application regardless of where the application is currently active.
Components Common to All LifeKeeper Configurations