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. This might require Prometheus to create a new chunk if needed. prometheus-promql query based on label value, Select largest label value in Prometheus query, Prometheus Query Overall average under a time interval, Prometheus endpoint of all available metrics. website 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! How to react to a students panic attack in an oral exam? Prometheus's query language supports basic logical and arithmetic operators. What is the point of Thrower's Bandolier? Return all time series with the metric http_requests_total: Return all time series with the metric http_requests_total and the given Our HTTP response will now show more entries: As we can see we have an entry for each unique combination of labels. Thank you for subscribing! This helps us avoid a situation where applications are exporting thousands of times series that arent really needed. When Prometheus sends an HTTP request to our application it will receive this response: This format and underlying data model are both covered extensively in Prometheus' own documentation. How to tell which packages are held back due to phased updates. Is it a bug? Lets create a demo Kubernetes cluster and set up Prometheus to monitor it. What am I doing wrong here in the PlotLegends specification? This patchset consists of two main elements. By default we allow up to 64 labels on each time series, which is way more than most metrics would use. 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. 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. count(ALERTS) or (1-absent(ALERTS)), Alternatively, count(ALERTS) or vector(0). This is what i can see on Query Inspector. Theres no timestamp anywhere actually. But the key to tackling high cardinality was better understanding how Prometheus works and what kind of usage patterns will be problematic. The region and polygon don't match. what does the Query Inspector show for the query you have a problem with? I.e., there's no way to coerce no datapoints to 0 (zero)? Prometheus query check if value exist. count the number of running instances per application like this: This documentation is open-source. Monitoring Docker container metrics using cAdvisor, Use file-based service discovery to discover scrape targets, Understanding and using the multi-target exporter pattern, Monitoring Linux host metrics with the Node Exporter. attacks, keep I used a Grafana transformation which seems to work. or Internet application, Samples are compressed using encoding that works best if there are continuous updates. We covered some of the most basic pitfalls in our previous blog post on Prometheus - Monitoring our monitoring. You're probably looking for the absent function. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. PROMQL: how to add values when there is no data returned? Prometheus is an open-source monitoring and alerting software that can collect metrics from different infrastructure and applications. 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. How do I align things in the following tabular environment? Does Counterspell prevent from any further spells being cast on a given turn? 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. Once configured, your instances should be ready for access. If you're looking for a 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. This would happen if any time series was no longer being exposed by any application and therefore there was no scrape that would try to append more samples to it. If we configure a sample_limit of 100 and our metrics response contains 101 samples, then Prometheus wont scrape anything at all. I cant see how absent() may help me here @juliusv yeah, I tried count_scalar() but I can't use aggregation with it. This allows Prometheus to scrape and store thousands of samples per second, our biggest instances are appending 550k samples per second, while also allowing us to query all the metrics simultaneously. Often it doesnt require any malicious actor to cause cardinality related problems. Before running the query, create a Pod with the following specification: Before running the query, create a PersistentVolumeClaim with the following specification: This will get stuck in Pending state as we dont have a storageClass called manual" in our cluster. In our example we have two labels, content and temperature, and both of them can have two different values. With any monitoring system its important that youre able to pull out the right data. 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. 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. without any dimensional information. Returns a list of label values for the label in every metric. Please help improve it by filing issues or pull requests. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. name match a certain pattern, in this case, all jobs that end with server: All regular expressions in Prometheus use RE2 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. https://grafana.com/grafana/dashboards/2129. You can query Prometheus metrics directly with its own query language: PromQL. entire corporate networks, This is the standard flow with a scrape that doesnt set any sample_limit: With our patch we tell TSDB that its allowed to store up to N time series in total, from all scrapes, at any time. This thread has been automatically locked since there has not been any recent activity after it was closed. While the sample_limit patch stops individual scrapes from using too much Prometheus capacity, which could lead to creating too many time series in total and exhausting total Prometheus capacity (enforced by the first patch), which would in turn affect all other scrapes since some new time series would have to be ignored. I'm sure there's a proper way to do this, but in the end, I used label_replace to add an arbitrary key-value label to each sub-query that I wished to add to the original values, and then applied an or to each. Run the following commands in both nodes to configure the Kubernetes repository. 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. 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. 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. Examples This works well if errors that need to be handled are generic, for example Permission Denied: But if the error string contains some task specific information, for example the name of the file that our application didnt have access to, or a TCP connection error, then we might easily end up with high cardinality metrics this way: Once scraped all those time series will stay in memory for a minimum of one hour. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. When using Prometheus defaults and assuming we have a single chunk for each two hours of wall clock we would see this: Once a chunk is written into a block it is removed from memSeries and thus from memory. Run the following commands in both nodes to install kubelet, kubeadm, and kubectl. Of course, this article is not a primer on PromQL; you can browse through the PromQL documentation for more in-depth knowledge. source, what your query is, what the query inspector shows, and any other About an argument in Famine, Affluence and Morality. Variable of the type Query allows you to query Prometheus for a list of metrics, labels, or label values. Not the answer you're looking for? rev2023.3.3.43278. Blocks will eventually be compacted, which means that Prometheus will take multiple blocks and merge them together to form a single block that covers a bigger time range. This means that our memSeries still consumes some memory (mostly labels) but doesnt really do anything. Extra metrics exported by Prometheus itself tell us if any scrape is exceeding the limit and if that happens we alert the team responsible for it. To do that, run the following command on the master node: Next, create an SSH tunnel between your local workstation and the master node by running the following command on your local machine: If everything is okay at this point, you can access the Prometheus console at http://localhost:9090. What does remote read means in Prometheus? What is the point of Thrower's Bandolier? Basically our labels hash is used as a primary key inside TSDB. No error message, it is just not showing the data while using the JSON file from that website. If you do that, the line will eventually be redrawn, many times over. I'm displaying Prometheus query on a Grafana table. Prometheus metrics can have extra dimensions in form of labels. All rights reserved. So I still can't use that metric in calculations ( e.g., success / (success + fail) ) as those calculations will return no datapoints. I can get the deployments in the dev, uat, and prod environments using this query: So we can see that tenant 1 has 2 deployments in 2 different environments, whereas the other 2 have only one. This garbage collection, among other things, will look for any time series without a single chunk and remove it from memory. Your needs or your customers' needs will evolve over time and so you cant just draw a line on how many bytes or cpu cycles it can consume. 11 Queries | Kubernetes Metric Data with PromQL, wide variety of applications, infrastructure, APIs, databases, and other sources. After a few hours of Prometheus running and scraping metrics we will likely have more than one chunk on our time series: Since all these chunks are stored in memory Prometheus will try to reduce memory usage by writing them to disk and memory-mapping. Ive deliberately kept the setup simple and accessible from any address for demonstration. but viewed in the tabular ("Console") view of the expression browser. Prometheus simply counts how many samples are there in a scrape and if thats more than sample_limit allows it will fail the scrape. In the following steps, you will create a two-node Kubernetes cluster (one master and one worker) in AWS. It will return 0 if the metric expression does not return anything. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Use Prometheus to monitor app performance metrics. Or maybe we want to know if it was a cold drink or a hot one? 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 is optional, but may be useful if you don't already have an APM, or would like to use our templates and sample queries. I know prometheus has comparison operators but I wasn't able to apply them. Now comes the fun stuff. Internally all time series are stored inside a map on a structure called Head. as text instead of as an image, more people will be able to read it and help. Redoing the align environment with a specific formatting. If the error message youre getting (in a log file or on screen) can be quoted Once we appended sample_limit number of samples we start to be selective. The result is a table of failure reason and its count. We also limit the length of label names and values to 128 and 512 characters, which again is more than enough for the vast majority of scrapes. Having a working monitoring setup is a critical part of the work we do for our clients. I believe it's the logic that it's written, but is there any . Can airtags be tracked from an iMac desktop, with no iPhone? Is there a solutiuon to add special characters from software and how to do it. @juliusv Thanks for clarifying that. If you look at the HTTP response of our example metric youll see that none of the returned entries have timestamps. 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. Connect and share knowledge within a single location that is structured and easy to search. Prometheus provides a functional query language called PromQL (Prometheus Query Language) that lets the user select and aggregate time series data in real time. Each time series stored inside Prometheus (as a memSeries instance) consists of: The amount of memory needed for labels will depend on the number and length of these. In order to make this possible, it's necessary to tell Prometheus explicitly to not trying to match any labels by . Hmmm, upon further reflection, I'm wondering if this will throw the metrics off. Please see data model and exposition format pages for more details. how have you configured the query which is causing problems? You can run a variety of PromQL queries to pull interesting and actionable metrics from your Kubernetes cluster. Improving your monitoring setup by integrating Cloudflares analytics data into Prometheus and Grafana Pint is a tool we developed to validate our Prometheus alerting rules and ensure they are always working website In both nodes, edit the /etc/hosts file to add the private IP of the nodes. The main motivation seems to be that dealing with partially scraped metrics is difficult and youre better off treating failed scrapes as incidents. Passing sample_limit is the ultimate protection from high cardinality. Does a summoned creature play immediately after being summoned by a ready action? node_cpu_seconds_total: This returns the total amount of CPU time. What can a lawyer do if the client wants him to be acquitted of everything despite serious evidence? If both the nodes are running fine, you shouldnt get any result for this query. This is one argument for not overusing labels, but often it cannot be avoided. which Operating System (and version) are you running it under? Both of the representations below are different ways of exporting the same time series: Since everything is a label Prometheus can simply hash all labels using sha256 or any other algorithm to come up with a single ID that is unique for each time series. If we have a scrape with sample_limit set to 200 and the application exposes 201 time series, then all except one final time series will be accepted. @rich-youngkin Yeah, what I originally meant with "exposing" a metric is whether it appears in your /metrics endpoint at all (for a given set of labels). 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. help customers build After a chunk was written into a block and removed from memSeries we might end up with an instance of memSeries that has no chunks. That map uses labels hashes as keys and a structure called memSeries as values. It will record the time it sends HTTP requests and use that later as the timestamp for all collected time series. 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). Lets pick client_python for simplicity, but the same concepts will apply regardless of the language you use. 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. Finally you will want to create a dashboard to visualize all your metrics and be able to spot trends. privacy statement. We use Prometheus to gain insight into all the different pieces of hardware and software that make up our global network. Find centralized, trusted content and collaborate around the technologies you use most. That's the query (Counter metric): sum(increase(check_fail{app="monitor"}[20m])) by (reason). Do roots of these polynomials approach the negative of the Euler-Mascheroni constant? Prometheus and PromQL (Prometheus Query Language) are conceptually very simple, but this means that all the complexity is hidden in the interactions between different elements of the whole metrics pipeline. The process of sending HTTP requests from Prometheus to our application is called scraping. This gives us confidence that we wont overload any Prometheus server after applying changes. This doesnt capture all complexities of Prometheus but gives us a rough estimate of how many time series we can expect to have capacity for. Run the following command on the master node: Once the command runs successfully, youll see joining instructions to add the worker node to the cluster. 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. Has 90% of ice around Antarctica disappeared in less than a decade? Each chunk represents a series of samples for a specific time range. However, if i create a new panel manually with a basic commands then i can see the data on the dashboard. These will give you an overall idea about a clusters health. Adding labels is very easy and all we need to do is specify their names. Asking for help, clarification, or responding to other answers. The Prometheus data source plugin provides the following functions you can use in the Query input field. want to sum over the rate of all instances, so we get fewer output time series, This is in contrast to a metric without any dimensions, which always gets exposed as exactly one present series and is initialized to 0. 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. This page will guide you through how to install and connect Prometheus and Grafana. The reason why we still allow appends for some samples even after were above sample_limit is that appending samples to existing time series is cheap, its just adding an extra timestamp & value pair. The simplest construct of a PromQL query is an instant vector selector. It saves these metrics as time-series data, which is used to create visualizations and alerts for IT teams. Every time we add a new label to our metric we risk multiplying the number of time series that will be exported to Prometheus as the result. rev2023.3.3.43278. Although, sometimes the values for project_id doesn't exist, but still end up showing up as one. Why are trials on "Law & Order" in the New York Supreme Court? Of course there are many types of queries you can write, and other useful queries are freely available. This scenario is often described as cardinality explosion - some metric suddenly adds a huge number of distinct label values, creates a huge number of time series, causes Prometheus to run out of memory and you lose all observability as a result. Knowing that it can quickly check if there are any time series already stored inside TSDB that have the same hashed value. Find centralized, trusted content and collaborate around the technologies you use most. To your second question regarding whether I have some other label on it, the answer is yes I do. Thats why what our application exports isnt really metrics or time series - its samples. These queries are a good starting point. The Graph tab allows you to graph a query expression over a specified range of time. Why do many companies reject expired SSL certificates as bugs in bug bounties? The Linux Foundation has registered trademarks and uses trademarks. Play with bool TSDB used in Prometheus is a special kind of database that was highly optimized for a very specific workload: This means that Prometheus is most efficient when continuously scraping the same time series over and over again. However, the queries you will see here are a baseline" audit. Since labels are copied around when Prometheus is handling queries this could cause significant memory usage increase. Timestamps here can be explicit or implicit. Monitor the health of your cluster and troubleshoot issues faster with pre-built dashboards that just work. Creating new time series on the other hand is a lot more expensive - we need to allocate new memSeries instances with a copy of all labels and keep it in memory for at least an hour. 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. Short story taking place on a toroidal planet or moon involving flying, How to handle a hobby that makes income in US, Doubling the cube, field extensions and minimal polynoms, Follow Up: struct sockaddr storage initialization by network format-string. By clicking Sign up for GitHub, you agree to our terms of service and After sending a request it will parse the response looking for all the samples exposed there. Any excess samples (after reaching sample_limit) will only be appended if they belong to time series that are already stored inside TSDB. I'm still out of ideas here. These queries will give you insights into node health, Pod health, cluster resource utilization, etc. Ive added a data source(prometheus) in Grafana. Run the following commands on the master node, only copy the kubeconfig and set up Flannel CNI. The second patch modifies how Prometheus handles sample_limit - with our patch instead of failing the entire scrape it simply ignores excess time series. Today, let's look a bit closer at the two ways of selecting data in PromQL: instant vector selectors and range vector selectors. I am interested in creating a summary of each deployment, where that summary is based on the number of alerts that are present for each deployment. Finally getting back to this. Is it suspicious or odd to stand by the gate of a GA airport watching the planes? Sign up and get Kubernetes tips delivered straight to your inbox. Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, How Intuit democratizes AI development across teams through reusability. So perhaps the behavior I'm running into applies to any metric with a label, whereas a metric without any labels would behave as @brian-brazil indicated? A sample is something in between metric and time series - its a time series value for a specific timestamp. 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.
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