Ceph Lab Components

The distinct hardware/software components that a lab is composed of and the way they interact between them is described here. In general, a lab is composed of a scheduler, worker(s), package builder (gitbuilder), job database (paddles), job archive, a web UI (pulpito) and test nodes.

Components of a Ceph Lab.

In the figure above, every service appears on a separate machine but this is not a requirement (see Teuthology Lab Setup Notes for an alternative setup). Jobs are submitted to the scheduler, which are then picked up by dispatcher and processesed by job supervisors. One supervisor processes and keeps track of a job (one at a time). The output of the job (logs and files associated to an execution) is stored in the archive, which is a path in the file system where the dispatcher is running. The job database contains information about the status of jobs and test nodes, as well as results of executions (# of tests passed, failed, etc.). All this information can be visualized in pulpito, the web UI. For an example, see Ceph community’s Lab here.

Test nodes can be grouped in classes (referred to as machine-type), allowing teuthology schedule jobs across multiple hardware setups.

Life of a Teuthology Job

The teuthology scheduler exposes a work queue (using beanstalkd) where jobs are submitted. The life of a job begins when teuthology-suite is executed, which is when a job is prepared and queued (teuthology-schedule is implicitly invoked). When a job is created (or whenever the status of a job is changed, e.g. from queued to started), information about the job is recorded in paddles’s internal database. Depending on the priority of the job, the scheduler eventually determines when a job can get executed. At this point, teuthology-dispatcher checks the lock status of the requested machines by querying paddles, acquires locks of the nodes if they are available, and invokes teuthology-dispatcher in supervisor mode. supervisor reimages the target machines and invokes teuthology (the command). teuthology proceeds to execute the job (execute every task in the YAML job description). After the execution is completed (ie teuthology process exits), supervisor unlocks the target machines. If the requested machines are not available, the dispatcher waits for the machines to be available before running anymore jobs. Results from the job are stored in the archive directory of the worker for forensic analysis.

Since QA suites usually specify install and ceph tasks, we briefly describe what they do. When a suite is scheduled (via teuthology-suite), the branch that is being worked against has to be specified (e.g. a git SHA or ref). Packages for the given branch and distro are probed on gitbuilder to see if they exist. Once this and other sanity checks pass, the job is created and scheduled. Once the job initializes, the install task pulls and installs Ceph packages from gitbuilder. The installation task might also be preceded by a kernel task which first reboots testnodes (and optionally installs) into a specified kernel. The ceph task subsequently configures and launches the cluster. At this point, Ceph is ready to receive requests from other tasks (such as rados).