Hi! I have a few thoughts on this KIP. First, I'd like to thank you for the writeup, clearly a lot of thought has gone into it and it is very thorough. However, I'm not convinced it's the right approach from a fundamental level.
Fundamentally, this KIP seems like somewhat of a solution to an organizational problem. Metrics are organizational concerns, not Kafka operator concerns. Clients should make it easy to plug in metrics (this is the approach I take in my own client), and organizations should have processes such that all clients gather and ship metrics how that organization desires. If an organization is set up correctly, there is no reason for metrics to be forwarded through Kafka. This feels like a solution to an organization not properly setting up how processes ship metrics, and in some ways, it's an overbroad solution, and in other ways, it doesn't cover the entire problem. >From the perspective of Kafka operators, it is easy to see that this KIP is nice in that it just dictates what clients should support for metrics and that the metrics should ship through Kafka. But, from the perspective of an observability team, this workflow is basically hijacking the standard flow that organizations may have. I would rather have applications collect metrics and ship them the same way every other application does. I'd rather not have to configure additional plugins within Kafka to take metrics and forward them. More importantly, this KIP prescibes cardinality problems, requires that to officially support the KIP a client must support all relevant metrics within the KIP, and requires that a client cannot support other metrics unless those other metrics also go through a KIP process. It is difficult to imagine all of these metrics being relevant to every organization, and there is no way for an organization to filter what is relevant within the client. Instead, the filtering is pushed downwards, meaning more network IO and more CPU costs to filter what is irrelevant and aggregate what needs to be aggregated, and more time for an organization to setup whatever it is that will be doing this filtering and aggregating. Contrast this with a client that enables hooking in to capture numbers that are relevant within an org itself: the org can gather what they want, ship only want they want, and ship directly to the observability system they have already set up. As an aside, it may also be wise to avoid shipping metrics through Kafka about client interaction with Kafka, because if Kafka is having problems, then orgs lose insight into those problems. This would be like statuspage using itself for status on its own systems. Another downside is that by dictating the important metrics, this KIP either has two choices: try to choose what is important to every org, and inevitably leave out something important to somebody else, or just add everything and let the orgs filter. This KIP mostly looks to go with the latter approach, meaning orgs will be shipping & filtering. With hooks, an org would be able to gather exactly what they want. As well, I expect that org applications have metrics on the state of the applications outside of the Kafka client. Applications are already sending non-Kafka-client related metrics outbound to observability systems. If a Kafka client provided hooks, then users could just gather the additional relevant Kafka client metrics and ship those metrics the same way they do all of their other metrics. It feels a bit odd for a Kafka client to have its own separate way of forwarding metrics. Another benefit hooks in clients is that organizations do not _have_ to set up additional plugins to forward metrics from Kafka. Hooks avoid extra organizational work. The option that the KIP provides for users of clients to opt out of metrics may avoid some of the above issues (by just disabling things at the user level), but that's not really great from the perspective of client authors, because the existence of this KIP forces authors to either just not implement the KIP, or increase complexity within the KIP. Further, from an operator perspective, if I would prefer clients to ship metrics through the systems they already have in place, now I have to expect that anything that uses librdkafka or the official Java client will be shipping me metrics that I have to deal with (since the KIP is default enabled). Lastly, I'm a little wary that this KIP may stem from a product goal of Confluent: since most everything uses librdkafka or the Java client, then by defaulting clients sending metrics, Confluent gets an easy way to provide metric panels for a nice cloud UI. If any client does not want to support these metrics, and then a user wonders why these hypothetical panels have no metrics, then Confluent can just reply "use a supported client". Even if this (potentially unlikely) scenario is true, then hooks would still be a great alternative, because then Confluent could provide drop-in hooks for any client and the end result of easy-panels would be the same. In summary, - Metrics are more of an organizational concern, not specifically a broker operator concern. - The proposal seems to hijack how metrics are gathered within organizations - I don't think KIPs should dictate which metrics should be gathered and which should not. Clients instead should make it easy for users to gather anything they could be interested in, and ignore anything they are not. - I think hooks are more extensible, more exact, and fit better into organizational workflows. On 2021/06/02 12:45:45, Magnus Edenhill <mag...@edenhill.se> wrote: > Hey all, > > I'm proposing KIP-714 to add remote Client metrics and observability. > This functionality will allow centralized monitoring and troubleshooting of > clients and their internals. > > Please see > https://cwiki.apache.org/confluence/display/KAFKA/KIP-714%3A+Client+metrics+and+observability > > Looking forward to your feedback! > > Regards, > Magnus >
