OCF (Open Cluster Framework)

OCF (Open Cluster Framework)
Name	OCF (Open Cluster Framework)
Developer	ClusterLabs, Linux-HA, SUSE, Red Hat
Released	2000s
Programming language	C, Shell
Operating system	Linux, Unix-like
License	LGPL, GPL

OCF (Open Cluster Framework) is a specification and set of conventions for High-availability cluster resource agents, integration, and interoperability between clustering stacks. It defines an interface for resource management, monitoring, and failover that allows resource scripts to be used across projects such as ClusterLabs, Pacemaker (software), Corosync, Heartbeat (software), DRBD, SUSE Linux Enterprise High Availability, and Red Hat High Availability offerings. The framework emphasizes portable, scriptable agents and standardized return codes so that diverse resources can be orchestrated by cluster managers from different vendors and communities.

Overview

OCF provides a formalized contract for resource agents that interact with cluster managers like Pacemaker (software), Heartbeat (software), Corosync, and distribution stacks from SUSE, Red Hat, Canonical (company), and community projects such as ClusterLabs. The specification prescribes action parameters, environment variables, exit codes, and metadata, enabling resources such as DRBD, Apache HTTP Server, PostgreSQL, MySQL, NFS, VIPs, and Filesystem handlers to behave predictably under orchestration by managers including crmsh, pcs (tool), and crm (Pacemaker) frontends. By decoupling agent semantics from cluster internals, OCF facilitates portability across implementations like OpenSUSE, Debian, CentOS, and Fedora deployments used by administrators from enterprises like Red Hat and research institutions using HPC infrastructures.

History and Development

The OCF began as a response to fragmentation among early clustering efforts such as Linux-HA, HeartBeat (software), and vendor-specific offerings from SUSE and Red Hat. Contributors from projects including ClusterLabs, Linux Kernel, DRBD Project, and community maintainers converged on a common agent model during the 2000s to reduce duplication and ease cross-project integration. Over time the specification evolved alongside cluster managers like Pacemaker (software) and messaging layers such as Corosync; major vendors including SUSE, Red Hat, and service providers in cloud ecosystems adopted OCF conventions to support standardized resource deployment. Community governance involved participants from Open Source initiatives, corporate engineers, and academic clusters cooperating through mailing lists, repositories, and issue trackers hosted on platforms used by projects such as GitHub and GitLab.

Architecture and Components

OCF centers on resource agent scripts or binaries that implement a defined set of actions (start, stop, monitor, promote, demote, meta-data), communicate via environment variables, and return standardized exit codes. The architecture connects resource agents to cluster managers such as Pacemaker (software) through standardized hooks and metadata blocks so orchestration logic—constraints, fencing, and location rules—can be applied consistently. Components typically include resource agents for services like DRBD, Apache HTTP Server, HAProxy, PostgreSQL, and Django (web framework) applications; cluster managers like Pacemaker (software); messaging layers like Corosync; fencing subsystems like STONITH implementations (e.g., ipmitool, fence_virt); and administrative tools including crmsh and pcs (tool).

Resource Agents and Scripts

Resource agents in OCF are usually implemented as executable scripts written in Bash (Unix shell), Python (programming language), or compiled C utilities and follow naming conventions (ocf:provider:resource). Each agent exposes actions such as start, stop, monitor, and meta-data and honors parameters declared for integration with frontends like crmsh and pcs (tool). Agents map operational states to OCF exit codes so managers like Pacemaker (software) can interpret health and recovery decisions; common agent examples include drivers for DRBD, network interfaces for IP virtual addresses, filesystem handlers for GFS2, and database connectors for MySQL and PostgreSQL. Projects like ClusterLabs maintain collections of agents to support interoperable stacks used by distributions such as OpenSUSE and CentOS.

Cluster Management and Policies

OCF enables cluster policies implemented in cluster managers such as Pacemaker (software) and used by admin tools like crmsh and pcs (tool). Policies include resource ordering, colocation constraints, failure policies, and recovery limits that reference OCF agent behavior. Integration with fencing and stonith plugins (for example via ipmitool or fence_virt) allows managers to enforce node isolation when agents report unrecoverable failures. OCF metadata assists policy engines in understanding agent capabilities—cloneable, promotable, and interleaveable—so managers can implement advanced topologies including active/passive, active/active, and master/slave configurations for services like PostgreSQL, DRBD, and NFS exports.

Implementations and Compatibility

Implementations of OCF conventions appear in resource agent repositories from ClusterLabs, distributions like SUSE Linux Enterprise, Red Hat Enterprise Linux, Debian, and community collections hosted by GitHub and GitLab. Compatibility is achieved through standardized metadata and exit codes which allow resource agents written for one manager to be used by another—e.g., an agent developed for Heartbeat (software) can often be deployed with Pacemaker (software) under Corosync messaging. Commercial support and testing by vendors such as SUSE, Red Hat, and cloud providers ensure agents work across virtualized platforms like KVM, Xen, and VMware vSphere.

Security and Reliability Considerations

OCF agents must be developed with privileges, authentication, and error handling in mind; best practices endorsed by vendors like Red Hat and SUSE include least-privilege execution, sandboxing, and explicit handling of transient versus permanent failures. Integration with fencing solutions such as STONITH and ipmitool is critical for split-brain prevention in distributed storage scenarios involving DRBD and clustered filesystems like GFS2. Reliability depends on proper timeout tuning, monitoring intervals, and testing under failure modes in environments used by organizations such as NASA, CERN, and enterprise datacenters run by Amazon Web Services or Microsoft Azure where high-availability guarantees are required. Security reviews typically involve code audits, package maintenance by distribution teams such as Debian and OpenSUSE, and adherence to operating-system level controls provided by SELinux and AppArmor.

Category:Clustering software