count(ALERTS) or (1-absent(ALERTS)), Alternatively, count(ALERTS) or vector(0). By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 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 Is it a bug? There is a single time series for each unique combination of metrics labels. Secondly this calculation is based on all memory used by Prometheus, not only time series data, so its just an approximation. All regular expressions in Prometheus use RE2 syntax. job and handler labels: Return a whole range of time (in this case 5 minutes up to the query time) Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Simple succinct answer. With 1,000 random requests we would end up with 1,000 time series in Prometheus. How To Query Prometheus on Ubuntu 14.04 Part 1 - DigitalOcean count(container_last_seen{name="container_that_doesn't_exist"}), What did you see instead? rev2023.3.3.43278. What can a lawyer do if the client wants him to be acquitted of everything despite serious evidence? One Head Chunk - containing up to two hours of the last two hour wall clock slot. As we mentioned before a time series is generated from metrics. Especially when dealing with big applications maintained in part by multiple different teams, each exporting some metrics from their part of the stack. attacks, keep Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, How Intuit democratizes AI development across teams through reusability. Prometheus Authors 2014-2023 | Documentation Distributed under CC-BY-4.0. The result is a table of failure reason and its count. Prometheus provides a functional query language called PromQL (Prometheus Query Language) that lets the user select and aggregate time series data in real time. You signed in with another tab or window. If we configure a sample_limit of 100 and our metrics response contains 101 samples, then Prometheus wont scrape anything at all. Ive added a data source(prometheus) in Grafana. 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. count(container_last_seen{environment="prod",name="notification_sender.*",roles=".application-server."}) One of the first problems youre likely to hear about when you start running your own Prometheus instances is cardinality, with the most dramatic cases of this problem being referred to as cardinality explosion. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Here at Labyrinth Labs, we put great emphasis on monitoring. 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. How to show that an expression of a finite type must be one of the finitely many possible values? Of course, this article is not a primer on PromQL; you can browse through the PromQL documentation for more in-depth knowledge. Asking for help, clarification, or responding to other answers. Returns a list of label values for the label in every metric. node_cpu_seconds_total: This returns the total amount of CPU time. 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. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. How is Jesus " " (Luke 1:32 NAS28) different from a prophet (, Luke 1:76 NAS28)? This works fine when there are data points for all queries in the expression. Its the chunk responsible for the most recent time range, including the time of our scrape. How can i turn no data to zero in Loki - Grafana Loki - Grafana Labs Using a query that returns "no data points found" in an - GitHub Thanks for contributing an answer to Stack Overflow! By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. I used a Grafana transformation which seems to work. Does Counterspell prevent from any further spells being cast on a given turn? Selecting data from Prometheus's TSDB forms the basis of almost any useful PromQL query before . vishnur5217 May 31, 2020, 3:44am 1. I suggest you experiment more with the queries as you learn, and build a library of queries you can use for future projects. Will this approach record 0 durations on every success? Combined thats a lot of different metrics. 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. Even Prometheus' own client libraries had bugs that could expose you to problems like this. The number of time series depends purely on the number of labels and the number of all possible values these labels can take. Already on GitHub? So there would be a chunk for: 00:00 - 01:59, 02:00 - 03:59, 04:00 . For Prometheus to collect this metric we need our application to run an HTTP server and expose our metrics there. Since this happens after writing a block, and writing a block happens in the middle of the chunk window (two hour slices aligned to the wall clock) the only memSeries this would find are the ones that are orphaned - they received samples before, but not anymore. For example, if someone wants to modify sample_limit, lets say by changing existing limit of 500 to 2,000, for a scrape with 10 targets, thats an increase of 1,500 per target, with 10 targets thats 10*1,500=15,000 extra time series that might be scraped. Once TSDB knows if it has to insert new time series or update existing ones it can start the real work. This process is also aligned with the wall clock but shifted by one hour. This would inflate Prometheus memory usage, which can cause Prometheus server to crash, if it uses all available physical memory. 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). whether someone is able to help out. If we make a single request using the curl command: We should see these time series in our application: But what happens if an evil hacker decides to send a bunch of random requests to our application? You can calculate how much memory is needed for your time series by running this query on your Prometheus server: Note that your Prometheus server must be configured to scrape itself for this to work. 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. By default we allow up to 64 labels on each time series, which is way more than most metrics would use. Run the following commands in both nodes to disable SELinux and swapping: Also, change SELINUX=enforcing to SELINUX=permissive in the /etc/selinux/config file. What this means is that a single metric will create one or more time series. to your account, What did you do? However when one of the expressions returns no data points found the result of the entire expression is no data points found. Before that, Vinayak worked as a Senior Systems Engineer at Singapore Airlines. We had a fair share of problems with overloaded Prometheus instances in the past and developed a number of tools that help us deal with them, including custom patches. Run the following commands on the master node, only copy the kubeconfig and set up Flannel CNI. or something like that. Our metrics are exposed as a HTTP response. 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. Bulk update symbol size units from mm to map units in rule-based symbology. I have a data model where some metrics are namespaced by client, environment and deployment name. However, the queries you will see here are a baseline" audit. If the time series already exists inside TSDB then we allow the append to continue. notification_sender-. Connect and share knowledge within a single location that is structured and easy to search. PROMQL: how to add values when there is no data returned? There is an open pull request which improves memory usage of labels by storing all labels as a single string. accelerate any Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2. To select all HTTP status codes except 4xx ones, you could run: http_requests_total {status!~"4.."} Subquery Return the 5-minute rate of the http_requests_total metric for the past 30 minutes, with a resolution of 1 minute. If you're looking for a For example, the following query will show the total amount of CPU time spent over the last two minutes: And the query below will show the total number of HTTP requests received in the last five minutes: There are different ways to filter, combine, and manipulate Prometheus data using operators and further processing using built-in functions. Inside the Prometheus configuration file we define a scrape config that tells Prometheus where to send the HTTP request, how often and, optionally, to apply extra processing to both requests and responses. or Internet application, ward off DDoS Already on GitHub? That's the query (Counter metric): sum(increase(check_fail{app="monitor"}[20m])) by (reason). Name the nodes as Kubernetes Master and Kubernetes Worker. Sign in The TSDB limit patch protects the entire Prometheus from being overloaded by too many time series. The more labels you have and the more values each label can take, the more unique combinations you can create and the higher the cardinality. Lets pick client_python for simplicity, but the same concepts will apply regardless of the language you use. VictoriaMetrics has other advantages compared to Prometheus, ranging from massively parallel operation for scalability, better performance, and better data compression, though what we focus on for this blog post is a rate () function handling. 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. If your expression returns anything with labels, it won't match the time series generated by vector(0). This garbage collection, among other things, will look for any time series without a single chunk and remove it from memory. Time arrow with "current position" evolving with overlay number. You can verify this by running the kubectl get nodes command on the master node. This means that looking at how many time series an application could potentially export, and how many it actually exports, gives us two completely different numbers, which makes capacity planning a lot harder. Prometheus simply counts how many samples are there in a scrape and if thats more than sample_limit allows it will fail the scrape. Prometheus metrics can have extra dimensions in form of labels. Explanation: Prometheus uses label matching in expressions. See these docs for details on how Prometheus calculates the returned results. help customers build The second patch modifies how Prometheus handles sample_limit - with our patch instead of failing the entire scrape it simply ignores excess time series. To better handle problems with cardinality its best if we first get a better understanding of how Prometheus works and how time series consume memory. By default Prometheus will create a chunk per each two hours of wall clock. but it does not fire if both are missing because than count() returns no data the workaround is to additionally check with absent() but it's on the one hand annoying to double-check on each rule and on the other hand count should be able to "count" zero . Have a question about this project? Cadvisors on every server provide container names. rev2023.3.3.43278. SSH into both servers and run the following commands to install Docker. Our HTTP response will now show more entries: As we can see we have an entry for each unique combination of labels. First is the patch that allows us to enforce a limit on the total number of time series TSDB can store at any time. Is there a single-word adjective for "having exceptionally strong moral principles"? Once it has a memSeries instance to work with it will append our sample to the Head Chunk. Lets adjust the example code to do this. We will examine their use cases, the reasoning behind them, and some implementation details you should be aware of. Why is this sentence from The Great Gatsby grammatical? Or maybe we want to know if it was a cold drink or a hot one? Then you must configure Prometheus scrapes in the correct way and deploy that to the right Prometheus server. Prometheus query check if value exist. Find centralized, trusted content and collaborate around the technologies you use most. We have hundreds of data centers spread across the world, each with dedicated Prometheus servers responsible for scraping all metrics. Cardinality is the number of unique combinations of all labels. Please dont post the same question under multiple topics / subjects. want to sum over the rate of all instances, so we get fewer output time series, gabrigrec September 8, 2021, 8:12am #8. Is it plausible for constructed languages to be used to affect thought and control or mold people towards desired outcomes? Is it suspicious or odd to stand by the gate of a GA airport watching the planes? 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. I'm displaying Prometheus query on a Grafana table. If a law is new but its interpretation is vague, can the courts directly ask the drafters the intent and official interpretation of their law? Asking for help, clarification, or responding to other answers. Today, let's look a bit closer at the two ways of selecting data in PromQL: instant vector selectors and range vector selectors. The more labels we have or the more distinct values they can have the more time series as a result. Lets say we have an application which we want to instrument, which means add some observable properties in the form of metrics that Prometheus can read from our application. Often it doesnt require any malicious actor to cause cardinality related problems. Using a query that returns "no data points found" in an expression. There are a number of options you can set in your scrape configuration block. We know that each time series will be kept in memory. 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! 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. Simply adding a label with two distinct values to all our metrics might double the number of time series we have to deal with. Monitor Confluence with Prometheus and Grafana | Confluence Data Center So the maximum number of time series we can end up creating is four (2*2). And then there is Grafana, which comes with a lot of built-in dashboards for Kubernetes monitoring. Is what you did above (failures.WithLabelValues) an example of "exposing"? In Prometheus pulling data is done via PromQL queries and in this article we guide the reader through 11 examples that can be used for Kubernetes specifically. without any dimensional information. This means that Prometheus must check if theres already a time series with identical name and exact same set of labels present. 1 Like. Do roots of these polynomials approach the negative of the Euler-Mascheroni constant? I've added a data source (prometheus) in Grafana. Monitor the health of your cluster and troubleshoot issues faster with pre-built dashboards that just work. In order to make this possible, it's necessary to tell Prometheus explicitly to not trying to match any labels by . Why do many companies reject expired SSL certificates as bugs in bug bounties? I don't know how you tried to apply the comparison operators, but if I use this very similar query: I get a result of zero for all jobs that have not restarted over the past day and a non-zero result for jobs that have had instances restart. new career direction, check out our open Theres only one chunk that we can append to, its called the Head Chunk. Prometheus has gained a lot of market traction over the years, and when combined with other open-source tools like Grafana, it provides a robust monitoring solution. your journey to Zero Trust. I can't work out how to add the alerts to the deployments whilst retaining the deployments for which there were no alerts returned: If I use sum with or, then I get this, depending on the order of the arguments to or: If I reverse the order of the parameters to or, I get what I am after: But I'm stuck now if I want to do something like apply a weight to alerts of a different severity level, e.g. our free app that makes your Internet faster and safer. The thing with a metric vector (a metric which has dimensions) is that only the series for it actually get exposed on /metrics which have been explicitly initialized. Another reason is that trying to stay on top of your usage can be a challenging task. What is the point of Thrower's Bandolier? This is because once we have more than 120 samples on a chunk efficiency of varbit encoding drops. 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. ward off DDoS from and what youve done will help people to understand your problem. Is there a solutiuon to add special characters from software and how to do it. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Querying basics | Prometheus How to tell which packages are held back due to phased updates. Names and labels tell us what is being observed, while timestamp & value pairs tell us how that observable property changed over time, allowing us to plot graphs using this data. Grafana renders "no data" when instant query returns empty dataset by (geo_region) < bool 4 Setting label_limit provides some cardinality protection, but even with just one label name and huge number of values we can see high cardinality. for the same vector, making it a range vector: Note that an expression resulting in a range vector cannot be graphed directly, PROMQL: how to add values when there is no data returned? or Internet application, To learn more about our mission to help build a better Internet, start here. So it seems like I'm back to square one. A time series that was only scraped once is guaranteed to live in Prometheus for one to three hours, depending on the exact time of that scrape. positions. Please see data model and exposition format pages for more details. After sending a request it will parse the response looking for all the samples exposed there. I'd expect to have also: Please use the prometheus-users mailing list for questions. how have you configured the query which is causing problems? It saves these metrics as time-series data, which is used to create visualizations and alerts for IT teams. Operating such a large Prometheus deployment doesnt come without challenges. Add field from calculation Binary operation. The Graph tab allows you to graph a query expression over a specified range of time. Which in turn will double the memory usage of our Prometheus server. Returns a list of label names. Asking for help, clarification, or responding to other answers. Use Prometheus to monitor app performance metrics. Any excess samples (after reaching sample_limit) will only be appended if they belong to time series that are already stored inside TSDB. Stumbled onto this post for something else unrelated, just was +1-ing this :). Even i am facing the same issue Please help me on this. This selector is just a metric name. 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. Prometheus is an open-source monitoring and alerting software that can collect metrics from different infrastructure and applications. There's also count_scalar(), I cant see how absent() may help me here @juliusv yeah, I tried count_scalar() but I can't use aggregation with it. list, which does not convey images, so screenshots etc. But the key to tackling high cardinality was better understanding how Prometheus works and what kind of usage patterns will be problematic. If both the nodes are running fine, you shouldnt get any result for this query. 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. metric name, as measured over the last 5 minutes: Assuming that the http_requests_total time series all have the labels job

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