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Cardinality is the number of unique combinations of all labels. Prometheus simply counts how many samples are there in a scrape and if thats more than sample_limit allows it will fail the scrape. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. The simplest construct of a PromQL query is an instant vector selector. which version of Grafana are you using? Separate metrics for total and failure will work as expected. more difficult for those people to help. to your account, What did you do? However, the queries you will see here are a baseline" audit. Have a question about this project? To this end, I set up the query to instant so that the very last data point is returned but, when the query does not return a value - say because the server is down and/or no scraping took place - the stat panel produces no data. On Thu, Dec 15, 2016 at 6:24 PM, Lior Goikhburg ***@***. an EC2 regions with application servers running docker containers. Now, lets install Kubernetes on the master node using kubeadm. By default we allow up to 64 labels on each time series, which is way more than most metrics would use. That response will have a list of, When Prometheus collects all the samples from our HTTP response it adds the timestamp of that collection and with all this information together we have a. but viewed in the tabular ("Console") view of the expression browser. This is the last line of defense for us that avoids the risk of the Prometheus server crashing due to lack of memory. In addition to that in most cases we dont see all possible label values at the same time, its usually a small subset of all possible combinations. Thanks, or Internet application, You can use these queries in the expression browser, Prometheus HTTP API, or visualization tools like Grafana. So the maximum number of time series we can end up creating is four (2*2). list, which does not convey images, so screenshots etc. Finally we maintain a set of internal documentation pages that try to guide engineers through the process of scraping and working with metrics, with a lot of information thats specific to our environment. Even Prometheus' own client libraries had bugs that could expose you to problems like this. This is the modified flow with our patch: By running go_memstats_alloc_bytes / prometheus_tsdb_head_series query we know how much memory we need per single time series (on average), we also know how much physical memory we have available for Prometheus on each server, which means that we can easily calculate the rough number of time series we can store inside Prometheus, taking into account the fact the theres garbage collection overhead since Prometheus is written in Go: memory available to Prometheus / bytes per time series = our capacity. Cadvisors on every server provide container names. Sign up and get Kubernetes tips delivered straight to your inbox. prometheus promql Share Follow edited Nov 12, 2020 at 12:27 If instead of beverages we tracked the number of HTTP requests to a web server, and we used the request path as one of the label values, then anyone making a huge number of random requests could force our application to create a huge number of time series. This garbage collection, among other things, will look for any time series without a single chunk and remove it from memory. Im new at Grafan and Prometheus. It saves these metrics as time-series data, which is used to create visualizations and alerts for IT teams. How do I align things in the following tabular environment? The real power of Prometheus comes into the picture when you utilize the alert manager to send notifications when a certain metric breaches a threshold. Going back to our metric with error labels we could imagine a scenario where some operation returns a huge error message, or even stack trace with hundreds of lines. Managed Service for Prometheus Cloud Monitoring Prometheus # ! The subquery for the deriv function uses the default resolution. gabrigrec September 8, 2021, 8:12am #8. rev2023.3.3.43278. In order to make this possible, it's necessary to tell Prometheus explicitly to not trying to match any labels by . Does a summoned creature play immediately after being summoned by a ready action? Once it has a memSeries instance to work with it will append our sample to the Head Chunk. Is there a single-word adjective for "having exceptionally strong moral principles"? This process helps to reduce disk usage since each block has an index taking a good chunk of disk space. This is because once we have more than 120 samples on a chunk efficiency of varbit encoding drops. If a sample lacks any explicit timestamp then it means that the sample represents the most recent value - its the current value of a given time series, and the timestamp is simply the time you make your observation at. Its not difficult to accidentally cause cardinality problems and in the past weve dealt with a fair number of issues relating to it. I then hide the original query. To your second question regarding whether I have some other label on it, the answer is yes I do. And then there is Grafana, which comes with a lot of built-in dashboards for Kubernetes monitoring. You can query Prometheus metrics directly with its own query language: PromQL. See these docs for details on how Prometheus calculates the returned results. There is an open pull request on the Prometheus repository. The nature of simulating nature: A Q&A with IBM Quantum researcher Dr. Jamie We've added a "Necessary cookies only" option to the cookie consent popup. Variable of the type Query allows you to query Prometheus for a list of metrics, labels, or label values. How to filter prometheus query by label value using greater-than, PromQL - Prometheus - query value as label, Why time duration needs double dot for Prometheus but not for Victoria metrics, How do you get out of a corner when plotting yourself into a corner. If we try to append a sample with a timestamp higher than the maximum allowed time for current Head Chunk, then TSDB will create a new Head Chunk and calculate a new maximum time for it based on the rate of appends. If I now tack on a != 0 to the end of it, all zero values are filtered out: Thanks for contributing an answer to Stack Overflow! If you look at the HTTP response of our example metric youll see that none of the returned entries have timestamps. Thats why what our application exports isnt really metrics or time series - its samples. Here at Labyrinth Labs, we put great emphasis on monitoring. To learn more, see our tips on writing great answers. Next you will likely need to create recording and/or alerting rules to make use of your time series. The text was updated successfully, but these errors were encountered: It's recommended not to expose data in this way, partially for this reason. Or do you have some other label on it, so that the metric still only gets exposed when you record the first failued request it? In this article, you will learn some useful PromQL queries to monitor the performance of Kubernetes-based systems. entire corporate networks, How to show that an expression of a finite type must be one of the finitely many possible values? For that lets follow all the steps in the life of a time series inside Prometheus. Also the link to the mailing list doesn't work for me. Subscribe to receive notifications of new posts: Subscription confirmed. What does remote read means in Prometheus? Do new devs get fired if they can't solve a certain bug? @zerthimon The following expr works for me The main motivation seems to be that dealing with partially scraped metrics is difficult and youre better off treating failed scrapes as incidents. At the same time our patch gives us graceful degradation by capping time series from each scrape to a certain level, rather than failing hard and dropping all time series from affected scrape, which would mean losing all observability of affected applications. The containers are named with a specific pattern: notification_checker [0-9] notification_sender [0-9] I need an alert when the number of container of the same pattern (eg. Prometheus is a great and reliable tool, but dealing with high cardinality issues, especially in an environment where a lot of different applications are scraped by the same Prometheus server, can be challenging. This is an example of a nested subquery. I'm displaying Prometheus query on a Grafana table. Prometheus allows us to measure health & performance over time and, if theres anything wrong with any service, let our team know before it becomes a problem. This page will guide you through how to install and connect Prometheus and Grafana. Minimising the environmental effects of my dyson brain. Prometheus query check if value exist. How is Jesus " " (Luke 1:32 NAS28) different from a prophet (, Luke 1:76 NAS28)? This article covered a lot of ground. If both the nodes are running fine, you shouldnt get any result for this query. These will give you an overall idea about a clusters health. Asking for help, clarification, or responding to other answers. Chunks will consume more memory as they slowly fill with more samples, after each scrape, and so the memory usage here will follow a cycle - we start with low memory usage when the first sample is appended, then memory usage slowly goes up until a new chunk is created and we start again. Since labels are copied around when Prometheus is handling queries this could cause significant memory usage increase. Object, url:api/datasources/proxy/2/api/v1/query_range?query=wmi_logical_disk_free_bytes%7Binstance%3D~%22%22%2C%20volume%20!~%22HarddiskVolume.%2B%22%7D&start=1593750660&end=1593761460&step=20&timeout=60s, Powered by Discourse, best viewed with JavaScript enabled, 1 Node Exporter for Prometheus Dashboard EN 20201010 | Grafana Labs, https://grafana.com/grafana/dashboards/2129. I'm still out of ideas here. Since we know that the more labels we have the more time series we end up with, you can see when this can become a problem. Its also worth mentioning that without our TSDB total limit patch we could keep adding new scrapes to Prometheus and that alone could lead to exhausting all available capacity, even if each scrape had sample_limit set and scraped fewer time series than this limit allows. But before that, lets talk about the main components of Prometheus. For instance, the following query would return week-old data for all the time series with node_network_receive_bytes_total name: node_network_receive_bytes_total offset 7d Those limits are there to catch accidents and also to make sure that if any application is exporting a high number of time series (more than 200) the team responsible for it knows about it. In general, having more labels on your metrics allows you to gain more insight, and so the more complicated the application you're trying to monitor, the more need for extra labels. Often it doesnt require any malicious actor to cause cardinality related problems. With any monitoring system its important that youre able to pull out the right data. Also, providing a reasonable amount of information about where youre starting The main reason why we prefer graceful degradation is that we want our engineers to be able to deploy applications and their metrics with confidence without being subject matter experts in Prometheus. rev2023.3.3.43278. This thread has been automatically locked since there has not been any recent activity after it was closed. In the screenshot below, you can see that I added two queries, A and B, but only . Other Prometheus components include a data model that stores the metrics, client libraries for instrumenting code, and PromQL for querying the metrics. PromQL allows you to write queries and fetch information from the metric data collected by Prometheus. Prometheus provides a functional query language called PromQL (Prometheus Query Language) that lets the user select and aggregate time series data in real time. This is one argument for not overusing labels, but often it cannot be avoided. We know that time series will stay in memory for a while, even if they were scraped only once. Once Prometheus has a list of samples collected from our application it will save it into TSDB - Time Series DataBase - the database in which Prometheus keeps all the time series. Adding labels is very easy and all we need to do is specify their names. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. This single sample (data point) will create a time series instance that will stay in memory for over two and a half hours using resources, just so that we have a single timestamp & value pair. Prometheus Authors 2014-2023 | Documentation Distributed under CC-BY-4.0. Finally you will want to create a dashboard to visualize all your metrics and be able to spot trends. Today, let's look a bit closer at the two ways of selecting data in PromQL: instant vector selectors and range vector selectors. as text instead of as an image, more people will be able to read it and help. The result of an expression can either be shown as a graph, viewed as tabular data in Prometheus's expression browser, or consumed by external systems via the HTTP API. The nature of simulating nature: A Q&A with IBM Quantum researcher Dr. Jamie We've added a "Necessary cookies only" option to the cookie consent popup. Lets adjust the example code to do this. The problem is that the table is also showing reasons that happened 0 times in the time frame and I don't want to display them. Well be executing kubectl commands on the master node only. positions. As we mentioned before a time series is generated from metrics. Any other chunk holds historical samples and therefore is read-only. It saves these metrics as time-series data, which is used to create visualizations and alerts for IT teams. If we were to continuously scrape a lot of time series that only exist for a very brief period then we would be slowly accumulating a lot of memSeries in memory until the next garbage collection. In the following steps, you will create a two-node Kubernetes cluster (one master and one worker) in AWS. Once configured, your instances should be ready for access. following for every instance: we could get the top 3 CPU users grouped by application (app) and process But before doing that it needs to first check which of the samples belong to the time series that are already present inside TSDB and which are for completely new time series. Have a question about this project? The struct definition for memSeries is fairly big, but all we really need to know is that it has a copy of all the time series labels and chunks that hold all the samples (timestamp & value pairs). Timestamps here can be explicit or implicit. To learn more, see our tips on writing great answers. However when one of the expressions returns no data points found the result of the entire expression is no data points found.In my case there haven't been any failures so rio_dashorigin_serve_manifest_duration_millis_count{Success="Failed"} returns no data points found.Is there a way to write the query so that a . Explanation: Prometheus uses label matching in expressions. At this point, both nodes should be ready. Play with bool Can airtags be tracked from an iMac desktop, with no iPhone? - I am using this in windows 10 for testing, which Operating System (and version) are you running it under? count(ALERTS) or (1-absent(ALERTS)), Alternatively, count(ALERTS) or vector(0). There is a single time series for each unique combination of metrics labels. Is it plausible for constructed languages to be used to affect thought and control or mold people towards desired outcomes? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. I've created an expression that is intended to display percent-success for a given metric. This selector is just a metric name. If we try to visualize how the perfect type of data Prometheus was designed for looks like well end up with this: A few continuous lines describing some observed properties. Is it possible to create a concave light? For that reason we do tolerate some percentage of short lived time series even if they are not a perfect fit for Prometheus and cost us more memory. Visit 1.1.1.1 from any device to get started with Having better insight into Prometheus internals allows us to maintain a fast and reliable observability platform without too much red tape, and the tooling weve developed around it, some of which is open sourced, helps our engineers avoid most common pitfalls and deploy with confidence. It enables us to enforce a hard limit on the number of time series we can scrape from each application instance. how have you configured the query which is causing problems? By default Prometheus will create a chunk per each two hours of wall clock. Thank you for subscribing! A metric can be anything that you can express as a number, for example: To create metrics inside our application we can use one of many Prometheus client libraries. What can a lawyer do if the client wants him to be acquitted of everything despite serious evidence? What can a lawyer do if the client wants him to be acquitted of everything despite serious evidence? Time arrow with "current position" evolving with overlay number. Well occasionally send you account related emails. accelerate any I'd expect to have also: Please use the prometheus-users mailing list for questions. Then imported a dashboard from " 1 Node Exporter for Prometheus Dashboard EN 20201010 | Grafana Labs ".Below is my Dashboard which is showing empty results.So kindly check and suggest. This helps us avoid a situation where applications are exporting thousands of times series that arent really needed. In the same blog post we also mention one of the tools we use to help our engineers write valid Prometheus alerting rules. In this blog post well cover some of the issues one might encounter when trying to collect many millions of time series per Prometheus instance. Why are trials on "Law & Order" in the New York Supreme Court? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. To make things more complicated you may also hear about samples when reading Prometheus documentation. scheduler exposing these metrics about the instances it runs): The same expression, but summed by application, could be written like this: If the same fictional cluster scheduler exposed CPU usage metrics like the So I still can't use that metric in calculations ( e.g., success / (success + fail) ) as those calculations will return no datapoints. These checks are designed to ensure that we have enough capacity on all Prometheus servers to accommodate extra time series, if that change would result in extra time series being collected. What happens when somebody wants to export more time series or use longer labels? To avoid this its in general best to never accept label values from untrusted sources. By default Prometheus will create a chunk per each two hours of wall clock. Each Prometheus is scraping a few hundred different applications, each running on a few hundred servers. If this query also returns a positive value, then our cluster has overcommitted the memory. Lets see what happens if we start our application at 00:25, allow Prometheus to scrape it once while it exports: And then immediately after the first scrape we upgrade our application to a new version: At 00:25 Prometheus will create our memSeries, but we will have to wait until Prometheus writes a block that contains data for 00:00-01:59 and runs garbage collection before that memSeries is removed from memory, which will happen at 03:00. In our example case its a Counter class object. TSDB will try to estimate when a given chunk will reach 120 samples and it will set the maximum allowed time for current Head Chunk accordingly. The most basic layer of protection that we deploy are scrape limits, which we enforce on all configured scrapes. Having good internal documentation that covers all of the basics specific for our environment and most common tasks is very important. Simple, clear and working - thanks a lot. Its very easy to keep accumulating time series in Prometheus until you run out of memory. rev2023.3.3.43278. For example our errors_total metric, which we used in example before, might not be present at all until we start seeing some errors, and even then it might be just one or two errors that will be recorded. To get a better understanding of the impact of a short lived time series on memory usage lets take a look at another example. Note that using subqueries unnecessarily is unwise. The below posts may be helpful for you to learn more about Kubernetes and our company. Although, sometimes the values for project_id doesn't exist, but still end up showing up as one. Setting label_limit provides some cardinality protection, but even with just one label name and huge number of values we can see high cardinality. PromQL allows querying historical data and combining / comparing it to the current data. Ive added a data source(prometheus) in Grafana. ncdu: What's going on with this second size column? and can help you on This means that Prometheus must check if theres already a time series with identical name and exact same set of labels present. This is because the Prometheus server itself is responsible for timestamps. I've been using comparison operators in Grafana for a long while. You can run a variety of PromQL queries to pull interesting and actionable metrics from your Kubernetes cluster. I'm not sure what you mean by exposing a metric. Please see data model and exposition format pages for more details. The Prometheus data source plugin provides the following functions you can use in the Query input field. First is the patch that allows us to enforce a limit on the total number of time series TSDB can store at any time. count the number of running instances per application like this: This documentation is open-source. AFAIK it's not possible to hide them through Grafana. Here is the extract of the relevant options from Prometheus documentation: Setting all the label length related limits allows you to avoid a situation where extremely long label names or values end up taking too much memory. Knowing that it can quickly check if there are any time series already stored inside TSDB that have the same hashed value. About an argument in Famine, Affluence and Morality. new career direction, check out our open your journey to Zero Trust. For example, this expression notification_sender-. I have a query that gets a pipeline builds and its divided by the number of change request open in a 1 month window, which gives a percentage. What sort of strategies would a medieval military use against a fantasy giant? Prometheus lets you query data in two different modes: The Console tab allows you to evaluate a query expression at the current time. Neither of these solutions seem to retain the other dimensional information, they simply produce a scaler 0. Looking at memory usage of such Prometheus server we would see this pattern repeating over time: The important information here is that short lived time series are expensive. Heres a screenshot that shows exact numbers: Thats an average of around 5 million time series per instance, but in reality we have a mixture of very tiny and very large instances, with the biggest instances storing around 30 million time series each. It doesnt get easier than that, until you actually try to do it. This is because the only way to stop time series from eating memory is to prevent them from being appended to TSDB. Any excess samples (after reaching sample_limit) will only be appended if they belong to time series that are already stored inside TSDB. Chunks that are a few hours old are written to disk and removed from memory. This process is also aligned with the wall clock but shifted by one hour. Our patched logic will then check if the sample were about to append belongs to a time series thats already stored inside TSDB or is it a new time series that needs to be created. Secondly this calculation is based on all memory used by Prometheus, not only time series data, so its just an approximation. VictoriaMetrics handles rate () function in the common sense way I described earlier! After sending a request it will parse the response looking for all the samples exposed there. Prometheus is an open-source monitoring and alerting software that can collect metrics from different infrastructure and applications. The speed at which a vehicle is traveling. Why is this sentence from The Great Gatsby grammatical? Monitor the health of your cluster and troubleshoot issues faster with pre-built dashboards that just work. The number of times some specific event occurred. information which you think might be helpful for someone else to understand To get rid of such time series Prometheus will run head garbage collection (remember that Head is the structure holding all memSeries) right after writing a block. If the time series doesnt exist yet and our append would create it (a new memSeries instance would be created) then we skip this sample. It will record the time it sends HTTP requests and use that later as the timestamp for all collected time series. By merging multiple blocks together, big portions of that index can be reused, allowing Prometheus to store more data using the same amount of storage space. Samples are stored inside chunks using "varbit" encoding which is a lossless compression scheme optimized for time series data. To select all HTTP status codes except 4xx ones, you could run: Return the 5-minute rate of the http_requests_total metric for the past 30 minutes, with a resolution of 1 minute.