This document is for a development version of Ceph.

Health Reports

How to Get Reports

In general, there are two channels to retrieve the health reports:

ceph (CLI)

which sends health mon command for retrieving the health status of the cluster

mgr module

which calls mgr.get('health') for the same report in the form of a JSON encoded string

The following diagrams outline the involved parties and how the interact when the clients query for the reports:

Where are the Reports Generated

Aggregator of Aggregators

Health reports are aggregated from multiple Paxos services:

  • AuthMonitor

  • HealthMonitor

  • MDSMonitor

  • MgrMonitor

  • MgrStatMonitor

  • MonmapMonitor

  • OSDMonitor

When persisting the pending changes in their own domain, each of them identifies the health related issues and store them into the monstore with the prefix of health using the same transaction. For instance, OSDMonitor checks a pending new osdmap for possible issues, like down OSDs and missing scrub flag in a pool, and then stores the encoded form of the health reports along with the new osdmap. These reports are later loaded and decoded, so they can be collected on demand. When it comes to MDSMonitor, it persists the health metrics in the beacon sent by the MDS daemons, and prepares health reports when storing the pending changes.

So, if we want to add a new warning related to cephfs, probably the best place to start is MDSMonitor::encode_pending(), where health reports are collected from the latest FSMap and the health metrics reported by MDS daemons.

But it’s noteworthy that MgrStatMonitor does not prepare the reports by itself, it just stores whatever the health reports received from mgr!

ceph-mgr -- A Delegate Aggregator

In Ceph, mgr is created to share the burden of monitor, which is used to establish the consensus of information which is critical to keep the cluster function. Apparently, osdmap, mdsmap and monmap fall into this category. But what about the aggregated statistics of the cluster? They are crucial for the administrator to understand the status of the cluster, but they might not be that important to keep the cluster running. To address this scalability issue, we offloaded the work of collecting and aggregating the metrics to mgr.

Now, mgr is responsible for receiving and processing the MPGStats messages from OSDs. And we also developed a protocol allowing a daemon to periodically report its metrics and status to mgr using MMgrReport. On the mgr side, it periodically sends an aggregated report to the MgrStatMonitor service on mon. As explained earlier, this service just persists the health reports in the aggregated report to the monstore.

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