prometheus query return 0 if no data

How is Jesus " " (Luke 1:32 NAS28) different from a prophet (, Luke 1:76 NAS28)? After running the query, a table will show the current value of each result time series (one table row per output series). I made the changes per the recommendation (as I understood it) and defined separate success and fail metrics. If our metric had more labels and all of them were set based on the request payload (HTTP method name, IPs, headers, etc) we could easily end up with millions of time series. Especially when dealing with big applications maintained in part by multiple different teams, each exporting some metrics from their part of the stack. Second rule does the same but only sums time series with status labels equal to "500". Connect and share knowledge within a single location that is structured and easy to search. Are there tables of wastage rates for different fruit and veg? So lets start by looking at what cardinality means from Prometheus' perspective, when it can be a problem and some of the ways to deal with it. Internally time series names are just another label called __name__, so there is no practical distinction between name and labels. I.e., there's no way to coerce no datapoints to 0 (zero)? Each chunk represents a series of samples for a specific time range. 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. We can use these to add more information to our metrics so that we can better understand whats going on. How Intuit democratizes AI development across teams through reusability. 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. The Head Chunk is never memory-mapped, its always stored in memory. How to follow the signal when reading the schematic? I was then able to perform a final sum by over the resulting series to reduce the results down to a single result, dropping the ad-hoc labels in the process. I have a data model where some metrics are namespaced by client, environment and deployment name. Going back to our time series - at this point Prometheus either creates a new memSeries instance or uses already existing memSeries. an EC2 regions with application servers running docker containers. No, only calling Observe() on a Summary or Histogram metric will add any observations (and only calling Inc() on a counter metric will increment it). @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). Prometheus metrics can have extra dimensions in form of labels. 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. To your second question regarding whether I have some other label on it, the answer is yes I do. I've added a data source (prometheus) in Grafana. Extra fields needed by Prometheus internals. Finally, please remember that some people read these postings as an email After sending a request it will parse the response looking for all the samples exposed there. Connect and share knowledge within a single location that is structured and easy to search. returns the unused memory in MiB for every instance (on a fictional cluster The way labels are stored internally by Prometheus also matters, but thats something the user has no control over. what does the Query Inspector show for the query you have a problem with? binary operators to them and elements on both sides with the same label set Its very easy to keep accumulating time series in Prometheus until you run out of memory. This is what i can see on Query Inspector. *) in region drops below 4. "no data". We use Prometheus to gain insight into all the different pieces of hardware and software that make up our global network. 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. In this article, you will learn some useful PromQL queries to monitor the performance of Kubernetes-based systems. As we mentioned before a time series is generated from metrics. syntax. So there would be a chunk for: 00:00 - 01:59, 02:00 - 03:59, 04:00 . Sign up for a free GitHub account to open an issue and contact its maintainers and the community. notification_sender-. Is it plausible for constructed languages to be used to affect thought and control or mold people towards desired outcomes? 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. Thirdly Prometheus is written in Golang which is a language with garbage collection. We know what a metric, a sample and a time series is. At this point we should know a few things about Prometheus: With all of that in mind we can now see the problem - a metric with high cardinality, especially one with label values that come from the outside world, can easily create a huge number of time series in a very short time, causing cardinality explosion. 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. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. 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. In the screenshot below, you can see that I added two queries, A and B, but only . as text instead of as an image, more people will be able to read it and help. A sample is something in between metric and time series - its a time series value for a specific timestamp. Lets create a demo Kubernetes cluster and set up Prometheus to monitor it. To set up Prometheus to monitor app metrics: Download and install Prometheus. how have you configured the query which is causing problems? That's the query (Counter metric): sum(increase(check_fail{app="monitor"}[20m])) by (reason). 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. 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. Operating such a large Prometheus deployment doesnt come without challenges. Use Prometheus to monitor app performance metrics. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. The next layer of protection is checks that run in CI (Continuous Integration) when someone makes a pull request to add new or modify existing scrape configuration for their application. The more labels we have or the more distinct values they can have the more time series as a result. Next you will likely need to create recording and/or alerting rules to make use of your time series. The most basic layer of protection that we deploy are scrape limits, which we enforce on all configured scrapes. Today, let's look a bit closer at the two ways of selecting data in PromQL: instant vector selectors and range vector selectors. attacks. accelerate any Explanation: Prometheus uses label matching in expressions. What is the point of Thrower's Bandolier? Simple, clear and working - thanks a lot. 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. Internally all time series are stored inside a map on a structure called Head. 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. without any dimensional information. 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. following for every instance: we could get the top 3 CPU users grouped by application (app) and process the problem you have. 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. That's the query ( Counter metric): sum (increase (check_fail {app="monitor"} [20m])) by (reason) The result is a table of failure reason and its count. For example, this expression First rule will tell Prometheus to calculate per second rate of all requests and sum it across all instances of our server. Why is this sentence from The Great Gatsby grammatical? We know that the more labels on a metric, the more time series it can create. It enables us to enforce a hard limit on the number of time series we can scrape from each application instance. 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. Samples are stored inside chunks using "varbit" encoding which is a lossless compression scheme optimized for time series data. This means that our memSeries still consumes some memory (mostly labels) but doesnt really do anything. gabrigrec September 8, 2021, 8:12am #8. 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. 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. If you're looking for a Even Prometheus' own client libraries had bugs that could expose you to problems like this. 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. In AWS, create two t2.medium instances running CentOS. This means that Prometheus must check if theres already a time series with identical name and exact same set of labels present. Add field from calculation Binary operation. 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. What video game is Charlie playing in Poker Face S01E07? ncdu: What's going on with this second size column? 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 we add another label that can also have two values then we can now export up to eight time series (2*2*2). Find centralized, trusted content and collaborate around the technologies you use most. 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. The Linux Foundation has registered trademarks and uses trademarks. All they have to do is set it explicitly in their scrape configuration. Its not going to get you a quicker or better answer, and some people might Both rules will produce new metrics named after the value of the record field. Passing sample_limit is the ultimate protection from high cardinality. list, which does not convey images, so screenshots etc. Sign up and get Kubernetes tips delivered straight to your inbox. We know that time series will stay in memory for a while, even if they were scraped only once. Finally you will want to create a dashboard to visualize all your metrics and be able to spot trends. 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. One thing you could do though to ensure at least the existence of failure series for the same series which have had successes, you could just reference the failure metric in the same code path without actually incrementing it, like so: That way, the counter for that label value will get created and initialized to 0. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. @juliusv Thanks for clarifying that. In both nodes, edit the /etc/sysctl.d/k8s.conf file to add the following two lines: Then reload the IPTables config using the sudo sysctl --system command. I'm displaying Prometheus query on a Grafana table. Subscribe to receive notifications of new posts: Subscription confirmed. The containers are named with a specific pattern: I need an alert when the number of container of the same pattern (eg. I know prometheus has comparison operators but I wasn't able to apply them. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2, Show or hide query result depending on variable value in Grafana, Understanding the CPU Busy Prometheus query, Group Label value prefixes by Delimiter in Prometheus, Why time duration needs double dot for Prometheus but not for Victoria metrics, Using a Grafana Histogram with Prometheus Buckets. 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. Is that correct? PromQL allows you to write queries and fetch information from the metric data collected by Prometheus. Does a summoned creature play immediately after being summoned by a ready action? Well occasionally send you account related emails. This is an example of a nested subquery. 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. Each Prometheus is scraping a few hundred different applications, each running on a few hundred servers. 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 such a stack trace ended up as a label value it would take a lot more memory than other time series, potentially even megabytes. This garbage collection, among other things, will look for any time series without a single chunk and remove it from memory. It will return 0 if the metric expression does not return anything. Can I tell police to wait and call a lawyer when served with a search warrant? to your account, What did you do? This helps Prometheus query data faster since all it needs to do is first locate the memSeries instance with labels matching our query and then find the chunks responsible for time range of the query. 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. Of course, this article is not a primer on PromQL; you can browse through the PromQL documentation for more in-depth knowledge. 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. 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. Since the default Prometheus scrape interval is one minute it would take two hours to reach 120 samples. Once it has a memSeries instance to work with it will append our sample to the Head Chunk. Basically our labels hash is used as a primary key inside TSDB. Why are trials on "Law & Order" in the New York Supreme Court? Asking for help, clarification, or responding to other answers. By default Prometheus will create a chunk per each two hours of wall clock. Setting label_limit provides some cardinality protection, but even with just one label name and huge number of values we can see high cardinality. The region and polygon don't match. count(ALERTS) or (1-absent(ALERTS)), Alternatively, count(ALERTS) or vector(0). rev2023.3.3.43278. So the maximum number of time series we can end up creating is four (2*2). Prometheus lets you query data in two different modes: The Console tab allows you to evaluate a query expression at the current time. 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. Prometheus's query language supports basic logical and arithmetic operators. @zerthimon You might want to use 'bool' with your comparator 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. If you look at the HTTP response of our example metric youll see that none of the returned entries have timestamps. Just add offset to the query. Timestamps here can be explicit or implicit. 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. *) in region drops below 4. alert also has to fire if there are no (0) containers that match the pattern in region. What is the point of Thrower's Bandolier? 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? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Simple succinct answer. 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. Simply adding a label with two distinct values to all our metrics might double the number of time series we have to deal with. Why do many companies reject expired SSL certificates as bugs in bug bounties? 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. Also, providing a reasonable amount of information about where youre starting 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. We covered some of the most basic pitfalls in our previous blog post on Prometheus - Monitoring our monitoring. rev2023.3.3.43278. There will be traps and room for mistakes at all stages of this process. 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. The difference with standard Prometheus starts when a new sample is about to be appended, but TSDB already stores the maximum number of time series its allowed to have. The more any application does for you, the more useful it is, the more resources it might need. Is it possible to create a concave light? No error message, it is just not showing the data while using the JSON file from that website. what error message are you getting to show that theres a problem? Youll be executing all these queries in the Prometheus expression browser, so lets get started. In the same blog post we also mention one of the tools we use to help our engineers write valid Prometheus alerting rules. Is there a single-word adjective for "having exceptionally strong moral principles"? 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. It doesnt get easier than that, until you actually try to do it. If we configure a sample_limit of 100 and our metrics response contains 101 samples, then Prometheus wont scrape anything at all. Connect and share knowledge within a single location that is structured and easy to search. Well occasionally send you account related emails. type (proc) like this: Assuming this metric contains one time series per running instance, you could 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. which version of Grafana are you using? 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. In my case there haven't been any failures so rio_dashorigin_serve_manifest_duration_millis_count{Success="Failed"} returns no data points found. It might seem simple on the surface, after all you just need to stop yourself from creating too many metrics, adding too many labels or setting label values from untrusted sources. 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. In our example we have two labels, content and temperature, and both of them can have two different values. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. 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. By clicking Sign up for GitHub, you agree to our terms of service and 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. 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. Other Prometheus components include a data model that stores the metrics, client libraries for instrumenting code, and PromQL for querying the metrics. By setting this limit on all our Prometheus servers we know that it will never scrape more time series than we have memory for.

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