This document is for a development version of Ceph.
How to Get Reports
In general, there are two channels to retrieve the health reports:
- ceph (CLI)
healthmon command for retrieving the health status of the cluster
- mgr module
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:
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
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
MDSMonitor::encode_pending(), where health reports are collected from
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.