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. Are you not exposing the fail metric when there hasn't been a failure yet? With our example metric we know how many mugs were consumed, but what if we also want to know what kind of beverage it was? Is it possible to rotate a window 90 degrees if it has the same length and width? by (geo_region) < bool 4 or Internet application, ward off DDoS 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. ***> wrote: You signed in with another tab or window. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Is it a bug? 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. The way labels are stored internally by Prometheus also matters, but thats something the user has no control over. instance_memory_usage_bytes: This shows the current memory used. This had the effect of merging the series without overwriting any values. Or maybe we want to know if it was a cold drink or a hot one? The second patch modifies how Prometheus handles sample_limit - with our patch instead of failing the entire scrape it simply ignores excess time series. Youll be executing all these queries in the Prometheus expression browser, so lets get started. There will be traps and room for mistakes at all stages of this process. 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. count(ALERTS) or (1-absent(ALERTS)), Alternatively, count(ALERTS) or vector(0). Returns a list of label names. In reality though this is as simple as trying to ensure your application doesnt use too many resources, like CPU or memory - you can achieve this by simply allocating less memory and doing fewer computations. To your second question regarding whether I have some other label on it, the answer is yes I do. After running the query, a table will show the current value of each result time series (one table row per output series). Next, create a Security Group to allow access to the instances. What is the point of Thrower's Bandolier? what does the Query Inspector show for the query you have a problem with? 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. Passing sample_limit is the ultimate protection from high cardinality. This also has the benefit of allowing us to self-serve capacity management - theres no need for a team that signs off on your allocations, if CI checks are passing then we have the capacity you need for your applications. Finally, please remember that some people read these postings as an email what error message are you getting to show that theres a problem? The main motivation seems to be that dealing with partially scraped metrics is difficult and youre better off treating failed scrapes as incidents. our free app that makes your Internet faster and safer. These will give you an overall idea about a clusters health. 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. Has 90% of ice around Antarctica disappeared in less than a decade? 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. SSH into both servers and run the following commands to install Docker. Can airtags be tracked from an iMac desktop, with no iPhone? When Prometheus collects metrics it records the time it started each collection and then it will use it to write timestamp & value pairs for each time series. Do roots of these polynomials approach the negative of the Euler-Mascheroni constant? Select the query and do + 0. About an argument in Famine, Affluence and Morality. PromQL allows querying historical data and combining / comparing it to the current data. Ive added a data source(prometheus) in Grafana. Has 90% of ice around Antarctica disappeared in less than a decade? Have you fixed this issue? 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. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Prometheus provides a functional query language called PromQL (Prometheus Query Language) that lets the user select and aggregate time series data in real time. Is what you did above (failures.WithLabelValues) an example of "exposing"? Of course, this article is not a primer on PromQL; you can browse through the PromQL documentation for more in-depth knowledge. If you're looking for a 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. The subquery for the deriv function uses the default resolution. accelerate any Use Prometheus to monitor app performance metrics. Finally we do, by default, set sample_limit to 200 - so each application can export up to 200 time series without any action. These queries will give you insights into node health, Pod health, cluster resource utilization, etc. It enables us to enforce a hard limit on the number of time series we can scrape from each application instance. PromQL allows you to write queries and fetch information from the metric data collected by Prometheus. 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 you need to obtain raw samples, then a range query must be sent to /api/v1/query. You can use these queries in the expression browser, Prometheus HTTP API, or visualization tools like Grafana. source, what your query is, what the query inspector shows, and any other We protect These queries are a good starting point. How to show that an expression of a finite type must be one of the finitely many possible values? What this means is that using Prometheus defaults each memSeries should have a single chunk with 120 samples on it for every two hours of data. 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. rev2023.3.3.43278. In this article, you will learn some useful PromQL queries to monitor the performance of Kubernetes-based systems. rev2023.3.3.43278. First rule will tell Prometheus to calculate per second rate of all requests and sum it across all instances of our server. We know that the more labels on a metric, the more time series it can create. Is there a way to write the query so that a default value can be used if there are no data points - e.g., 0. Run the following commands on the master node, only copy the kubeconfig and set up Flannel CNI. The idea is that if done as @brian-brazil mentioned, there would always be a fail and success metric, because they are not distinguished by a label, but always are exposed. (fanout by job name) and instance (fanout by instance of the job), we might I'm displaying Prometheus query on a Grafana table. 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. Is a PhD visitor considered as a visiting scholar? If this query also returns a positive value, then our cluster has overcommitted the memory. 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. You must define your metrics in your application, with names and labels that will allow you to work with resulting time series easily. There is an open pull request on the Prometheus repository. Even Prometheus' own client libraries had bugs that could expose you to problems like this. privacy statement. For example, this expression 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. Here are two examples of instant vectors: You can also use range vectors to select a particular time range. The process of sending HTTP requests from Prometheus to our application is called scraping. Once theyre in TSDB its already too late. About an argument in Famine, Affluence and Morality. The Prometheus data source plugin provides the following functions you can use in the Query input field. privacy statement. Windows 10, how have you configured the query which is causing problems? Already on GitHub? website However, if i create a new panel manually with a basic commands then i can see the data on the dashboard. Redoing the align environment with a specific formatting. But the key to tackling high cardinality was better understanding how Prometheus works and what kind of usage patterns will be problematic. Samples are stored inside chunks using "varbit" encoding which is a lossless compression scheme optimized for time series data. The text was updated successfully, but these errors were encountered: This is correct. 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. 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. 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. All chunks must be aligned to those two hour slots of wall clock time, so if TSDB was building a chunk for 10:00-11:59 and it was already full at 11:30 then it would create an extra chunk for the 11:30-11:59 time range. What can a lawyer do if the client wants him to be acquitted of everything despite serious evidence? 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 Cardinality is the number of unique combinations of all labels. 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. Up until now all time series are stored entirely in memory and the more time series you have, the higher Prometheus memory usage youll see. 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. Making statements based on opinion; back them up with references or personal experience. 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. 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. 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. 02:00 - create a new chunk for 02:00 - 03:59 time range, 04:00 - create a new chunk for 04:00 - 05:59 time range, 22:00 - create a new chunk for 22:00 - 23:59 time range. Monitor the health of your cluster and troubleshoot issues faster with pre-built dashboards that just work. 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. Do new devs get fired if they can't solve a certain bug? Both patches give us two levels of protection. 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. What am I doing wrong here in the PlotLegends specification? With this simple code Prometheus client library will create a single metric. I'm still out of ideas here. Will this approach record 0 durations on every success? We know that each time series will be kept in memory. Since the default Prometheus scrape interval is one minute it would take two hours to reach 120 samples. without any dimensional information. Returns a list of label values for the label in every metric. If the total number of stored time series is below the configured limit then we append the sample as usual. Operating such a large Prometheus deployment doesnt come without challenges. Find centralized, trusted content and collaborate around the technologies you use most. You set up a Kubernetes cluster, installed Prometheus on it ,and ran some queries to check the clusters health. Please dont post the same question under multiple topics / subjects. If the error message youre getting (in a log file or on screen) can be quoted to get notified when one of them is not mounted anymore. Well be executing kubectl commands on the master node only. Internally all time series are stored inside a map on a structure called Head. I believe it's the logic that it's written, but is there any conditions that can be used if there's no data recieved it returns a 0. what I tried doing is putting a condition or an absent function,but not sure if thats the correct approach. However when one of the expressions returns no data points found the result of the entire expression is no data points found. You can verify this by running the kubectl get nodes command on the master node. The most basic layer of protection that we deploy are scrape limits, which we enforce on all configured scrapes. or something like that. Simply adding a label with two distinct values to all our metrics might double the number of time series we have to deal with. The Graph tab allows you to graph a query expression over a specified range of time. it works perfectly if one is missing as count() then returns 1 and the rule fires. Making statements based on opinion; back them up with references or personal experience. attacks. Cadvisors on every server provide container names. gabrigrec September 8, 2021, 8:12am #8. (pseudocode): This gives the same single value series, or no data if there are no alerts. With our custom patch we dont care how many samples are in a scrape. A simple request for the count (e.g., rio_dashorigin_memsql_request_fail_duration_millis_count) returns no datapoints). 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. 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. It will return 0 if the metric expression does not return anything. The containers are named with a specific pattern: I need an alert when the number of container of the same pattern (eg. With 1,000 random requests we would end up with 1,000 time series in Prometheus. 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. Asking for help, clarification, or responding to other answers. There's also count_scalar(), How to follow the signal when reading the schematic? In our example case its a Counter class object. *) in region drops below 4. Is that correct? To learn more, see our tips on writing great answers. new career direction, check out our open Have a question about this project? Also, providing a reasonable amount of information about where youre starting By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. But you cant keep everything in memory forever, even with memory-mapping parts of data. @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). To subscribe to this RSS feed, copy and paste this URL into your RSS reader. https://github.com/notifications/unsubscribe-auth/AAg1mPXncyVis81Rx1mIWiXRDe0E1Dpcks5rIXe6gaJpZM4LOTeb. The simplest way of doing this is by using functionality provided with client_python itself - see documentation here. your journey to Zero Trust. ward off DDoS