OCF Resource Agent

OCF Resource Agent
Name	OCF Resource Agent
Developer	Open Cluster Forum
Released	2000s
Programming language	C, Shell
Operating system	Linux, Unix-like
License	LGPL, BSD

OCF Resource Agent OCF Resource Agent is a specification and collection of scripts used to manage high-availability resources within cluster frameworks such as Pacemaker (software), Heartbeat (software), Corosync, DRBD and related projects. It provides a standardized interface for controlling, monitoring and recovering services and devices on nodes running Red Hat Enterprise Linux, Debian, Ubuntu (operating system), SUSE Linux Enterprise Server and other Unix-like distributions. The initiative is sponsored and maintained through the Open Cluster Forum and collaborates with projects like Linux Foundation initiatives and enterprise vendors including Canonical (company), SUSE, Red Hat, IBM and Oracle Corporation.

Overview

OCF Resource Agents define a set of actions (start, stop, monitor, promote, demote, validate-all, meta-data) and parameters so that cluster managers such as Pacemaker (software), Heartbeat (software), Corosync, and OpenAIS can manage heterogeneous resources including filesystems, IP addresses, databases and virtual machines. The model complements complementary technologies like DRBD for block replication, Kubernetes for container orchestration, Xen (hypervisor) and KVM (kernel-based virtual machine) for virtualization, and integrates with configuration tools from Ansible (software), Puppet (software), and Chef (software). OCF Resource Agents are often packaged in distributions maintained by vendors such as Red Hat, Inc., SUSE, Canonical (company), and community projects like ClusterLabs.

Architecture and Components

The specification distinguishes between metadata, action scripts and helper libraries. Typical components include an agent script written in Bourne shell or Python (programming language), a metadata XML block conforming to OCF schema, and support functions provided by libraries such as the Resource Agent library used by Pacemaker (software). Agents implement the standard action interface to be invoked by cluster managers such as crmsh or tooling from ClusterLabs. Resource types frequently covered include IPaddr2 (virtual IP), Filesystem, Systemd service units managed against systemd on distributions like Fedora, as well as database agents for PostgreSQL, MySQL, MariaDB and middleware like Apache HTTP Server, Nginx and HAProxy.

Development and Implementation

Development follows contributions to upstream repositories maintained by ClusterLabs and vendor-specific packaging in projects like Debian (operating system), Ubuntu (operating system), Red Hat Enterprise Linux, and SUSE Linux Enterprise Server. Authors and maintainers often include engineers from Red Hat, Inc., SUSE, Canonical (company), IBM, and community members active in Open Source Initiative ecosystems. Implementation requires adherence to the OCF specification for exit codes and environment variables, and interoperability testing with orchestration stacks like Pacemaker, Corosync, DRBD, and tooling such as crmsh and pcs (Pacemaker/Corosync).

Operation and Lifecycle

At runtime, cluster managers call agent actions to effect state changes during failover, fencing and recovery workflows coordinated with fencing mechanisms like STONITH, vendor implementations such as IPMI, and integration with monitoring systems like Nagios, Zabbix (software), Prometheus. Agents must return standardized exit codes and support idempotent operations to allow safe repeated invocations by controllers including Pacemaker (software), Heartbeat (software), and higher-level management systems like OpenStack compute and CloudStack. Lifecycle events span from initial validation and metadata discovery through start/stop transitions, monitor probes, and optional promote/demote actions for master/slave resources such as DRBD or clustered PostgreSQL deployments using tools like Patroni.

Standards and Compliance

OCF Resource Agents conform to specifications defined by the Open Cluster Forum and reference behaviors used by the Linux Standard Base historically, while interacting with system facilities developed by projects such as systemd and libc implementations like glibc. Compliance requires support for OCF environment variables, action semantics, and exit status conventions used by managers like Pacemaker (software), which is governed by the ClusterLabs community and enterprise vendors including Red Hat, Inc. and SUSE.

Use Cases and Examples

Common use cases include providing floating IP addresses with IPaddr2 for HAProxy or Apache HTTP Server frontends, controlling clustered filesystems like GFS2 or OCFS2 for Red Hat-based clusters, managing replicated storage via DRBD combined with Pacemaker for databases such as PostgreSQL and MySQL, and orchestrating virtual machine failover for KVM (kernel-based virtual machine), Xen (hypervisor), or VirtualBox integrations. Operators often combine OCF agents with configuration management from Ansible (software), Puppet (software), Chef (software), and monitoring from Prometheus or Nagios to build resilient services for enterprises like Netflix, Facebook, Google-like scale architectures adapted to private clouds and telco NFV scenarios.

Troubleshooting and Best Practices

Best practices include using vendor-provided agents from Red Hat, Inc., SUSE, Canonical (company), validating agent metadata with tools provided by ClusterLabs, testing idempotency against Pacemaker (software), and coordinating with fencing solutions like STONITH and IPMI. Troubleshooting steps often involve examining cluster logs from Pacemaker, Corosync, system logs managed by systemd-journald, and agent debug output. For complex services, recommended practices are to employ staged promotion/demotion testing with resources such as DRBD, perform chaos testing similar to techniques used by Netflix's resilience engineering teams, and integrate monitoring from Prometheus or Zabbix (software) to detect and automate recovery.

Category:High-availability software