Do we need to store all that telemetry?(mattklein123.dev) |
Do we need to store all that telemetry?(mattklein123.dev) |
I can't count the number of times users (or myself) discovered bug after many weeks because something gradually failed over time. Also it saves a lot of time to be able to pin point the exact day a behavior as changed so you can check the deploy of that day and quickly find the bug. Sometimes a trend is not obvious after a deploy but is clearly visible on the graph after a long period of time.
And for business intelligence, it's always when you badly need a metric that you realize you never tracked it.
But let's take the case of metrics as an example--do we need full sample granularity for "old" data? Do we need full tag cardinality? Sample granularity reduction could be done with a transform to rollups at a coarser time granularity. That's a 60x reduction going from Hz to 1/min. You might lose a bunch of frequency information this way, but maybe that's ok?
Numbers are really nice in ways that text is not.
I keep harping on this, but compressed utf-8 text (or even worse, compressed json) is a horribly wasteful way to do it. See [1]. Putting a small amount of thought into storing telemetry data seems like it could yield incredible savings at scale.
[1] https://lists.w3.org/Archives/Public/www-logging/1996May/000...
One great side effect of this was service developers weren't afraid to write logs. We logged excessively, and it didn't cost too much. If we'd been indexing everything in ES it would have bankrupted us.
These days with S3 and the cloud, hadoop (or the EMR suite) per se probably isn't the way to go, but I'd sure like to see observability solutions giving me a first-class programming model that I as a user can interact with--not some bespoke "query DSL", and for them to accept that instantaneous indexed retrieval isn't important.
This paper is really interesting: https://www.usenix.org/system/files/osdi21-rodrigues.pdf
Stuff like this gives me hope we can have it both ways. With highly tuned compression and programmatic access the user is empowered and the cost is minimized.
- converting every number into its sequence of digits in decimal notation,
- writing those one character at a time,
- also write the string representation of the label of each value repeatedly for every record,
- compress all this with a structure-unaware generic text compression algorithm based on longest match search.
Each time you want to read that data, undo all of the above in reverse order.
You can optimize to some degree, but that's basically it.
I expect that not doing any of this saves the time spent doing it. I also expect data type aware compression to be much more efficient than text compressing the text expansion.
In numbers, I expect 2 to 3 orders of magnitude difference in time and also in space (for non random data).
But jcgrillo was talking about storage (at least his link was). And when parsing for analysis or for storing millions of points daily, there's no doubt that a binary format is simply a lot more CPU and disk efficient.
127.0.0.1 user-identifier frank [10/Oct/2000:13:55:36 -0700] "GET /apache_pb.gif HTTP/1.0" 200 2326
Playing around with gzip -9 on some test data[2] (not exactly CLF, but maybe similar entropy) I'm getting like ~1.9x compression.
Obviously if I parse this log line into a JSON blob, that blob will compress with a much higher ratio due to the repetitive nature of JSON, but it'll still be larger than the equivalent compressed CLF.
I'm working on a demo for my "protobof + fst[3]" idea, so I'm not sure if my "maybe ~5x" claim is totally off the mark or not. But I'm confident we can do way better than JSON.
[1] https://en.wikipedia.org/wiki/Common_Log_Format [2] https://www.sec.gov/about/data/edgar-log-file-data-sets [3] https://crates.io/crates/fst
EDIT: I guess maybe another way to state my conjecture is "telemetry compression is not general purpose text compression". These data have a schema, and by ignoring that fact and treating them always as schemaless data (employing general purpose text compression methods) we're leaving something on the table.
I bet you a full dollar that both in-house and open source solutions, on average, are way more stingy with resources. As they should be.
I think that this is a good idea when storage is concern for high-volume logs / production. Persisting the buffer when high error rates / unusual system behavior is observed would be a cool idea.
OpenTelemetry recently ish gained Open Agent Management Protocol (OpAMP), which allows some runtime control over things generating telemetry. The ability to stay fairly low but then scale up as needed sounds tempting, but gee it also sends shivers down my spine thinking of having such a elastic demands on one's telemetry infrastructure, as engineers turn telemetry up as problems are occuring. https://opentelemetry.io/docs/specs/opamp/
The idea of having a local circular buffer sounds excellent to me. Being able to run local queries & aggregate would be sweet. Are there any open otel issues discussing these ideas?
It's also possible they collect too much in the wrong formats.
But the ability to vet a hypothesis (I bet our users are confused about feature X, which we can test by looking at how many times they go to page X, then Y, then X again in 30 second window) in an hour versus 2 sprints is vastly underappreciated/underutilized.
I feel like this article paints with too broad a brush.
From a systems standpoint do you need to have all resources stored centrally in order to do centralized reporting? No, of course not. Admittedly it's handy if bandwidth and storage are free. The alternative is distributed storage, with or without summarization at the edge (and aggregating from distributed storage for reporting).
Having it distributed does raise access issues: access needs to be controlled, and management of access needs to be managed. Philosophically the Cloud solutions sell centralized management, but federation is a perfectly viable option. The choice is largely dictated by organizational structure not technology.
There is also a difference between diagnostic and evaluative indicators. Trying to evaluate from diagnostics causes fatigue because humans aren't built that way; evaluatives can and should be built from diagnostics. Diagnostics can't be built from evaluatives.
The logging/telemetry stack that I propose is:
1) Ephemeral logging at the limits of whatever observability you can build. E.g.: systemd journal with a small backing store, similar to a ring buffer.
2) Your compliance framework may require shipping some classes of events off of the local host, but I don't think any of them require shipping it to the cloud.
3) Build evaluatives locally in Redis.
4) Use DNS to query those evaluatives from elsewhere for ad hoc as well as historical purposes. This could be a centralized location or it could be true federation where each site accesses all other site's evaluatives.
I wouldn't put Redis on the internet, but I don't worry too much about DNS; and there are well-understood ways of securing DNS from tampering, unauthorized access, and even observation. By the way, DNS will handle hundreds or thousands of queries per second you just have to build for it.
curl http://athena.m3047.net/grafitti.html
dig @athena.m3047.net grafitti\;*.keys.redis.athena.m3047 txtHas Matt read any prior art in this field? https://research.google/pubs/monarch-googles-planet-scale-in...
I couldn't agree with the author more. Keeping historical records of business metrics makes a ton of sense. But history telemetry (CPU, Memory, Network, error logs) makes little sense.
If an issue occurs, then turn on telemetry around that issue until you track it down. If an issue occurs once and never again, did it really matter? This obviously does not apply to security, I'm just speaking of operational issues.
Keeping all of your application logs and telemetry forever is expensive, and I can't recall a single time when having more than a day's with of history was ever useful in tracking down an operational issue.
1: https://www.forbes.com/sites/forbestechcouncil/2022/10/03/th...
Nobody needs to retain metrics like CPU, Memory for weeks but I may want to see their numbers during an incident, or not long after it is over.
If your CPU and memory aren't affecting the business metrics, then it's not super relevant.
Also consider the potential risks of handling personal data and leaks.
A day is a pretty small window, I'd say a week or a bit more is good enough for most orgs. That way you can compare specific endpoints/code between deploys, answering questions like "was this endpoint this slow last week too or did I break it?". Some issues take a few days to brew and having historical data is important in debugging. Many orgs don't do load testing at all or have any real performance analysis done before things crash.
Log retention is also directly tied to how fast and easily can you detect and recover from issues.
I disagree. Every issue I've ever debugged, I did a tail -f on the logs. I can't recall ever searching the old logs.
Even if it takes a few days for an issue to brew, usually the logs right now will show the issue. Or if they don't, then you can turn on the logs and have them in a few days time. It's so rare that it's almost never worth keeping the logs around just for that one case where an old log might lead to resolution, and rarely does one have time during an active incident to look at old logs anyway.
User writes into support 3 days after the problem occurred, and support goes back and forth covering level 1 possibilities for an additional 2 days before escalating. It's common for 1 support complaint to represent some larger factor of users who never complain, so it would be useful to understand how common the issue is once it has been identified in the observability data. Having one day isn't sufficient in this scenario.
Forever is probably too much, but keeping a month or so is totally sane.
Telemetry needs to be motivated for it to not be considered spyware. You need to really consider what you are logging and why, and then, is it worth the downsides.
It is not something to take lightly, hardly "no harm".
Have a look at the description and performance of a non-toy time series database published 10 years ago:
https://www.vldb.org/pvldb/vol8/p1816-teller.pdf
Convenience of text and json is an argument, but performance??
This blog post has some interesting ideas as well: https://www.uber.com/blog/reducing-logging-cost-by-two-order...
collecting user-identified telemetry is debatable (depends on the case), but not collecting anything at all is just plain stupid.
When the business metrics start to fail. You don't need constant metics on storage, you can poll it every so often. If your app is constrained by CPU or RAM, then the business metrics will reflect that, and then you can turn on collection of those metrics to identify the problem.
> i feel like you have never touched servers/backend in anything more than simple projects (or at all). with full storage/memory there could be an issue that you won't be able to ssh to the server, so it speaks about your knowledge in this matter.
I ran all of ops for reddit for four years and headed up SRE at Netflix, so I have some experience in large scale systems. Not that it should matter.
After having annoyed how many users and lost how much revenue? Having metrics to identify brewing problems before issues start to arise (be they on arriving CPU, memory, disk, network constraints or increasing network latency which will soon but not yet show up in the business metrics) is valuable.
> I ran all of ops for reddit for four years and headed up SRE at Netflix, so I have some experience in large scale systems. Not that it should matter.
I have a hard time believing at either of those it was acceptable to have a problem ongoing for days without any idea what's happening because logs and metrics weren't enabled in the first place.
…but why incur that round trip on my feedback loop? Having those metrics on doesn’t cost me much.
This feels potentially like the perspective of a large organisation with both mature monitoring systems and quite steady state user base activity (through scale). When I have a customer who had an issue yesterday because they had an unusual workload that won’t be repeated often, I can’t afford not to have had the basic metrics turned on, in case they point us in the right direction.
not having cpu/mem/hdd metrics is just plain bogus and sounds like fantasy world, where everything works like we expect it to work, and there is no bugs at all. ridiculous
It's happened to me a few times.
This service is using 80% CPU, that seems a bit high... but is it always this high? Looks like it spiked within the last hour. But wait, it does that every Monday at 9 am, so probably a red herring.
This cache has a hit ratio of 60%... is that good? A bit low? Actually it's suspiciously high compared to last week - looks like a lot of people aren't getting a personalised feed.
Metrics are incredibly cheap to keep around for the value you get from a good operational dashboard, despite what Datadog/Amazon/Grafana Cloud tells you. It's just the most egregiously overpriced data you can buy since 20 cent text messages.
A good start is to set up VictoriaMetrics with some collectors and set retention to 14 days.
Also, as your storage hits 97%+, you'll probably start seeing effects in your business metrics, and then you can look into it.
real-time, high precision metrics aren't necessary. when you say that you don't need metrics and then say that you can poll metrics periodically, you are contradicting yourself.
Unless you want to be able to have trends over time, either for capacity planning (needing to order more storage in case of bare metal, or planning costs ahead) or to correlate with other things (storage consumption is growing twice as fast since deployment X, did we change something there?).
You don't need to have 1s granularity metrics on storage consumption, but having none is just stupid levels of fake "optimisation" that will cost you more in the long run.
> i feel like you have never touched servers/backend in anything more than simple projects (or at all). with full storage/memory there could be an issue that you won't be able to ssh to the server, so it speaks about your knowledge in this matter.
He was answering that.
If instead of dismissing someone outright and question their competence, you had raised specific concerns, this would have been a more productive conversation
he first said that we don't need to monitor anything, just enable debugging when "business metrics" are failing, and then he changed his stance to "polling from time to time". that's just shows that his first take wasn't thoughtful, so I assumed that he never worked in "the field" or worked on smaller projects, as nobody that worked in bigger projects would say that "we don't need CPU/mem/hdd metrics". it's not like hes proposing something novel, that just ridiculous take that needs to be called out
I feel like if you are going to go out on a limb and call someone's expertise into question...
> I ran all of ops for reddit for four years and headed up SRE at Netflix
And they provide excellent credentials which you failed to check...
> where you worked doesn't matter to me very much
You can't just weasel out of it by pretending like you didn't start the interaction by calling someone's expertise into question.
that's logical fallacy, you can work in any place on earth and still be wrong in the subject.
> You can't just weasel out of it by pretending like you didn't start the interaction by calling someone's expertise into question.
why? if his take is bad, then his job or experience doesn't change the outcome. i'm not an expert by any means, but things that hes saying just contradict everything that is standard practice and my own experience. based on that i'm able to say that he doesn't know what he's saying/proposing, and using his "excellent credentials" just make things worse, as it shows that he doesn't have an argument, just wishful thinking
read again what is his argument, that we don't need to store __any__ cpu/mem/storage metrics, other than "business metrics" (or later he crawled back to polling from time to time).
> Look, I have a different opinion as well, but the difference between you and me is I'm not resorting to personal attacks and instead discussing it on the merits.
maybe that's due to difference in culture/region, but i'm unaware where i've attacked him personally. i've just pointed out that what he's saying is to be expected by someone without experience/knowledge "in the field".
> Keeping all of your application logs and telemetry forever is expensive, and I can't recall a single time when having more than a day's with of history was ever useful in tracking down an operational issue.
That doesn't say don't store any, that says you can get by storing a 24 hour period. And his broader point is that it should be time bound, that storing these metrics indefinitely isn't useful and can be very expensive.
I'm of the mind that a week or two of fast online access is the right amount myself (with offline "cold" storage of logs for a longer period), but the overall premise that storing logs and infrastructure metrics forever is unnecessary and wasteful.