On Mon, Apr 4, 2016 at 4:03 PM, John Sanda <jsanda@redhat.com> wrote:
Making sure we don’t break clients is the most important aspect of this; however, there are some other questions I want to throw out. Today we only support clients adding raw data points. What if in the future though we add support for complex types like histograms and allow clients to directly store them. Would clients post that data to /raw, /stats, or something else?

Today we compute aggregated metrics at query time. We are going to add support for pre-computed aggregate metrics that are persisted. Do we have different endpoints for each? I haven’t thought about it too much yet, but I don’t separate endpoints is the way to go.

In the actual JIRA ticket there were 3 ideas floated around: separate endpoint, or /raw endpoint (because that is not bucketed data), or /stats endpoint (because is bucketed, just server side). And I think those are all the possible variations. One thing that I do not like about '/data' and pre-computed aggregates, if we do not split that method will serve 3 or 4 different formats depending on query params. That is way too complicated for both us and the users.
 

With HWKMETRICS-373, we are introducing support for tag based bucketing as opposed to the date range bucketing already have. There are some minor differences in the data structures returned in the response, namely a map is returned instead of an array. Should we have a different endpoints for tag based buckets vs date range buckets?

I like the idea of just raw and stats. I associate /raw with raw data stored by Hawkular Metrics, and that includes pre-computed aggregates too, and /stats with some sort of statistical computation done do the raw data before returned to the user. Based on this, the tag querying would fall under '/stats' if data is bucketed and would fall under '/raw' if you query for just raw data that is tagged.
 

We currently have one increasingly complex method to handle queries for raw data, various permutations of date range buckets, and eventually tag based buckets once my changes for HWKMETRICS-373 are merged. These changes definitely will simplify things on the server side, but do they simply or otherwise improve things for clients? I am a little concerned that we might be letting our implementation bleed into the API a little too much. For example, we segment our data in our schema design by metric type. Do we necessarily need to do that everywhere in the API?

I like to think about the API in terms of code integration and not necessarily from the perspective of an actual end-user. To me the end-users will never see our interface, they just see some pretty UI. From an integration perspective serving multiple data formats over a single endpoint is not easy to accommodate on most frameworks. But we need to balance exploding the API into too many end-points. The explanation I wrote about raw and stats will help us keep the number of end-points under control.

One of the reasons the JIRA ticket was opened is Angular and their design of the REST framework. Serving multiple data formats over the same endpoint is a big no-no. And there is also a special limitation that you need to decided ahead of time if and end-point serves arrays or not; errors occur if you expect array but get single object and vice-versa. With this in mind, I think we need to focus on how consumable is our interface from a machine code perspective.

And here is one more perspective to think on this. The current API served us for the past year and a half. Are the changes proposed here going to go good for the next year and half? I think based on the roadmap that we published, the planned features, and the current code, these changes are a step in a good direction.


 

On Apr 4, 2016, at 10:21 AM, Matt Wringe <mwringe@redhat.com> wrote:

----- Original Message -----
From: "Heiko W.Rupp" <hrupp@redhat.com>
To: "Discussions around Hawkular development" <hawkular-dev@lists.jboss.org>
Sent: Monday, April 4, 2016 4:56:15 AM
Subject: Re: [Hawkular-dev] Hawkular Metrics - /data enpoint

On 2 Apr 2016, at 0:24, Stefan Negrea wrote:
The plan is to deprecate existing '*/data' endpoints in the upcoming
release (0.15.0) and remove them in the release after that (0.16.0). That
gives enough time (roughly 2 months) for all existing projects to migrate
to the newer API. Does anybody see any problem with this timeline?

Yes.
There are users out there that use the old api in production.
They may not even be aware that there is a new one.

If they deploy the new hawkular-metrics (or someone does
for them), their apps will break and they may not even know
why.

+1

I think we need to make sure that we don't break the existing API for current users who are already using it. There will most likely be a bunch of complaints if we update this in OpenShift and then everyone's setup stops working.

REST allows for content negotiation. So we should keep the
old endpoint, deprecate them (and perhaps even spit regular
warnings in the logs) and on top add the new endpoints
that you suggested but with a new content type
like "application/json+hawkular-v2".

If we are going to introduce a new version for the REST API, it might make sense to release Hawkular Metrics with a new major version as well. But major versions can be tricky depending on how the project handles them. Some projects will have the same major versions for years, others will update the major version almost monthly (eg kernel version versus browser version)

In fact if we keen old and new, that new content type
is not exactly needed if the data format exchanged does not
change.

Btw: I doubt that GET ../data and POST ../data is confusing anyone
and in Jax-Rs you can have those on two different methods anyway.
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