Hi Ernesto,
Thanks for your valuable inputs. Kindly find my answers inline below.
On Wed, Mar 22, 2023 at 6:11 AM Ernesto Puerta <epuertat@xxxxxxxxxx> wrote:
Hi Prashant,Is this move just limited to the impact of the cluster log in the mon store db or is it part of a larger mon db clean-up effort?
Yes, it's limited to moving cluster logs from the monstore db.
I'm asking this because, besides de cluster log, the mon store db is currently used (and perhaps abused) also by some mgr modules via:
- set_module_option() to set MODULE_OPTIONS values via CLI commands.
- set_store(): there are 2 main storage use cases here:
- Immutable/sensitive data: instead of exposing those as MODULE_OPTIONS (password hashes, private certificates, API keys, etc.),
- Changing data: mgr-module internal state. While this shouldn't cause the db to grow in the long term, it might cause short-term/compaction issues (I'm not familiar with rocksdb internals, just extrapolating from experience with sstable/leveldb)
The config related information stored in db should not be a problem here. We are only concerned about logm entries in the event of health error that too when logm entries are not getting trimmed.
For the latter case there, Dashboard developers have been looking for an efficient alternative to persistently store rapidly-changing data. We discarded the idea of using a pool since the Dashboard should be able to operate prior to any OSD provisioning and in case of storage downtimesComing back to your original questions, I understand that there are two different issues at stake:
- Cluster log processing: currently mon via Paxos (Do we really need Paxos ack for logs? Can we live with some type of eventually-consistent/best-effort storage here?)
Yes, we need paxos ack for logm. The logm entries gets written to monstore on paxos proposal and gets written to cluster log on update from paxos. Yes, we are working on different approaches and one of them is to write to the dedicated pool.
- Cluster log storage: currently mon store db. AFAIK this is the main issue, right?
Yes, that's right.
From there, I see 2 possible paths:
- Keep cluster-wide logs as a Ceph concern:
- IMHO putting some throttling in place should be a must, since client-triggered cluster logs could easily become a DoS vector.
- I wouldn't put them into a rados pool, not so much for the data availability in case of OSD service downtime (logs will still be recoverable from logfiles), but as for the potential interference with user workloads/deployment patterns (as Frank mentioned before).
- Could we run the ".mgr" pool on a new type of "internal/service-only" colocated OSDs (memstore)?
- Save logs to a fixed-size/TTL-bound priority or multi-level queue structure?
- Add some (eventually-consistent) store db to the ceph-mgr?
- To solve ceph-mgr scalability issues, we recently added a new kind of Ceph utility daemon (ceph-exporter) whose sole purpose is to fetch metrics from co-located Ceph daemon's perf-counters and make those available for Prometheus scraping. We could think about a similar thing but for logs... (although it'd be very similar to the Loki approach below).
- Move them outside Ceph:
- Cephadm + Dashboard now support Centralized Logging via Loki + Promtail, which basically polls all daemon logfiles and sends new log traces to a central service (Loki) where they can be monitored/filtered in real-time.
- If we find the previous solution too bulky for regular cluster monitoring, we could explore systemd-journal-remote/rsyslog/...
- The main downside of this approach is that it might break the "ceph log" command (rados_monitor_log and log events could still be watched I guess).
This is really helpful. Let me explore these paths. If required, we will propose a meeting with a wider audience to discuss this further.
Kind Regards,Ernesto
Regards,
Prashant
On Wed, Mar 22, 2023 at 11:12 AM Janne Johansson <icepic.dz@xxxxxxxxx> wrote:> 2) .mgr pool
>
> 2.1) I have become really tired of these administrative pools that are created on the fly without any regards to device classes, available capacity, PG allocation and the like. The first one that showed up without warning was device_health_metrics, which turned the cluster health_err right away because the on-the-fly pool creation is, well, not exactly smart.
>
> We don't even have drives below the default root. We have a lot of different pools on different (custom!) device classes with different replication schemes to accommodate a large variety of use cases. Administrative pools showing up randomly somewhere in the tree are a real pain. There are ceph-user cases where people deleted and recreated it only to make the device health module useless, because it seems to store the pool ID and there is no way to tell it to use the new pool.
>
Ah, that's why it looked unused after I also had to remake it. Since
it gets created when you don't have the OSDs yet, the possibilities
for it ending up wrong seem very large.
--
May the most significant bit of your life be positive.
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