Variable of the type Query allows you to query Prometheus for a list of metrics, labels, or label values. The most basic layer of protection that we deploy are scrape limits, which we enforce on all configured scrapes. Have a question about this project? See this article for details. @rich-youngkin Yes, the general problem is non-existent series. 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. If the error message youre getting (in a log file or on screen) can be quoted This garbage collection, among other things, will look for any time series without a single chunk and remove it from memory. count(ALERTS) or (1-absent(ALERTS)), Alternatively, count(ALERTS) or vector(0). 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 Confluence with Prometheus and Grafana | Confluence Data Center With 1,000 random requests we would end up with 1,000 time series in Prometheus. If your expression returns anything with labels, it won't match the time series generated by vector(0). returns the unused memory in MiB for every instance (on a fictional cluster Since the default Prometheus scrape interval is one minute it would take two hours to reach 120 samples. 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. We know what a metric, a sample and a time series is.
Both patches give us two levels of protection. This is one argument for not overusing labels, but often it cannot be avoided. Bulk update symbol size units from mm to map units in rule-based symbology. what error message are you getting to show that theres a problem? This holds true for a lot of labels that we see are being used by engineers. 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. To get a better idea of this problem lets adjust our example metric to track HTTP requests. 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. Sign in It will return 0 if the metric expression does not return anything. Youve learned about the main components of Prometheus, and its query language, PromQL.
How can i turn no data to zero in Loki - Grafana Loki - Grafana Labs But you cant keep everything in memory forever, even with memory-mapping parts of data. How to react to a students panic attack in an oral exam? 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. Will this approach record 0 durations on every success? your journey to Zero Trust. Do roots of these polynomials approach the negative of the Euler-Mascheroni constant? Even Prometheus' own client libraries had bugs that could expose you to problems like this. by (geo_region) < bool 4 What happens when somebody wants to export more time series or use longer labels? Stumbled onto this post for something else unrelated, just was +1-ing this :). 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. Its very easy to keep accumulating time series in Prometheus until you run out of memory. Under which circumstances? are going to make it This had the effect of merging the series without overwriting any values. Theres only one chunk that we can append to, its called the Head Chunk. Already on GitHub? 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. rev2023.3.3.43278. 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. The containers are named with a specific pattern: I need an alert when the number of container of the same pattern (eg. source, what your query is, what the query inspector shows, and any other *) in region drops below 4. alert also has to fire if there are no (0) containers that match the pattern in region. Internally all time series are stored inside a map on a structure called Head. So it seems like I'm back to square one. These are the sane defaults that 99% of application exporting metrics would never exceed. Selecting data from Prometheus's TSDB forms the basis of almost any useful PromQL query before . 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. I have just used the JSON file that is available in below website Connect and share knowledge within a single location that is structured and easy to search. Select the query and do + 0. Going back to our time series - at this point Prometheus either creates a new memSeries instance or uses already existing memSeries. 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. Making statements based on opinion; back them up with references or personal experience. Every two hours Prometheus will persist chunks from memory onto the disk. In AWS, create two
t2.medium instances running CentOS. Ive deliberately kept the setup simple and accessible from any address for demonstration. It's worth to add that if using Grafana you should set 'Connect null values' proeprty to 'always' in order to get rid of blank spaces in the graph. or Internet application, ward off DDoS 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. We know that the more labels on a metric, the more time series it can create. Already on GitHub? 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. 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. 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. bay, For example, /api/v1/query?query=http_response_ok [24h]&time=t would return raw samples on the time range (t-24h . 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. In order to make this possible, it's necessary to tell Prometheus explicitly to not trying to match any labels by . 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. 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. rev2023.3.3.43278. How can I group labels in a Prometheus query? privacy statement. Windows 10, how have you configured the query which is causing problems? count(container_last_seen{environment="prod",name="notification_sender.*",roles=".application-server."}) The simplest construct of a PromQL query is an instant vector selector. which outputs 0 for an empty input vector, but that outputs a scalar Yeah, absent() is probably the way to go. Sign in 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. There is a single time series for each unique combination of metrics labels. 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. 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. 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. With this simple code Prometheus client library will create a single metric. Good to know, thanks for the quick response! Has 90% of ice around Antarctica disappeared in less than a decade? There are a number of options you can set in your scrape configuration block. ncdu: What's going on with this second size column? PromLabs | Blog - Selecting Data in PromQL Subscribe to receive notifications of new posts: Subscription confirmed. following for every instance: we could get the top 3 CPU users grouped by application (app) and process Although, sometimes the values for project_id doesn't exist, but still end up showing up as one. 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. This process helps to reduce disk usage since each block has an index taking a good chunk of disk space. PROMQL: how to add values when there is no data returned? About an argument in Famine, Affluence and Morality. 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. 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. It saves these metrics as time-series data, which is used to create visualizations and alerts for IT teams. We know that time series will stay in memory for a while, even if they were scraped only once. Our HTTP response will now show more entries: As we can see we have an entry for each unique combination of labels. Connect and share knowledge within a single location that is structured and easy to search. 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. syntax. Once TSDB knows if it has to insert new time series or update existing ones it can start the real work. want to sum over the rate of all instances, so we get fewer output time series, Prometheus - exclude 0 values from query result - Stack Overflow Why do many companies reject expired SSL certificates as bugs in bug bounties? https://github.com/notifications/unsubscribe-auth/AAg1mPXncyVis81Rx1mIWiXRDe0E1Dpcks5rIXe6gaJpZM4LOTeb. Now, lets install Kubernetes on the master node using kubeadm. Well occasionally send you account related emails. 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. I then hide the original query. I have a data model where some metrics are namespaced by client, environment and deployment name. (pseudocode): summary = 0 + sum (warning alerts) + 2*sum (alerts (critical alerts)) This gives the same single value series, or no data if there are no alerts. Hmmm, upon further reflection, I'm wondering if this will throw the metrics off. Simply adding a label with two distinct values to all our metrics might double the number of time series we have to deal with. 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. Although you can tweak some of Prometheus' behavior and tweak it more for use with short lived time series, by passing one of the hidden flags, its generally discouraged to do so. And then there is Grafana, which comes with a lot of built-in dashboards for Kubernetes monitoring. You signed in with another tab or window. Ive added a data source(prometheus) in Grafana. For a list of trademarks of The Linux Foundation, please see our Trademark Usage page. As we mentioned before a time series is generated from metrics. Our metric will have a single label that stores the request path. Well be executing kubectl commands on the master node only. One or more for historical ranges - these chunks are only for reading, Prometheus wont try to append anything here. I am always registering the metric as defined (in the Go client library) by prometheus.MustRegister(). To get a better understanding of the impact of a short lived time series on memory usage lets take a look at another example. 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. 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. 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. But the real risk is when you create metrics with label values coming from the outside world. Asking for help, clarification, or responding to other answers. 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. 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. That map uses labels hashes as keys and a structure called memSeries as values. PROMQL: how to add values when there is no data returned? instance_memory_usage_bytes: This shows the current memory used. 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. If we configure a sample_limit of 100 and our metrics response contains 101 samples, then Prometheus wont scrape anything at all. Sign up and get Kubernetes tips delivered straight to your inbox. 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. Of course there are many types of queries you can write, and other useful queries are freely available. 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. But before that, lets talk about the main components of Prometheus. How is Jesus " " (Luke 1:32 NAS28) different from a prophet (, Luke 1:76 NAS28)? Cardinality is the number of unique combinations of all labels. Prometheus does offer some options for dealing with high cardinality problems. 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 patchset consists of two main elements. This is what i can see on Query Inspector. Prometheus will keep each block on disk for the configured retention period. See these docs for details on how Prometheus calculates the returned results. When you add dimensionality (via labels to a metric), you either have to pre-initialize all the possible label combinations, which is not always possible, or live with missing metrics (then your PromQL computations become more cumbersome). Having a working monitoring setup is a critical part of the work we do for our clients. Prometheus metrics can have extra dimensions in form of labels. This is the last line of defense for us that avoids the risk of the Prometheus server crashing due to lack of memory. Making statements based on opinion; back them up with references or personal experience. Samples are stored inside chunks using "varbit" encoding which is a lossless compression scheme optimized for time series data. 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. 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. The speed at which a vehicle is traveling. Vinayak is an experienced cloud consultant with a knack of automation, currently working with Cognizant Singapore. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. The second patch modifies how Prometheus handles sample_limit - with our patch instead of failing the entire scrape it simply ignores excess time series. Thirdly Prometheus is written in Golang which is a language with garbage collection. Why are trials on "Law & Order" in the New York Supreme Court? Before that, Vinayak worked as a Senior Systems Engineer at Singapore Airlines. Return the per-second rate for all time series with the http_requests_total A common class of mistakes is to have an error label on your metrics and pass raw error objects as values. Once configured, your instances should be ready for access. Lets pick client_python for simplicity, but the same concepts will apply regardless of the language you use. Please see data model and exposition format pages for more details. In this article, you will learn some useful PromQL queries to monitor the performance of Kubernetes-based systems. Run the following commands on the master node to set up Prometheus on the Kubernetes cluster: Next, run this command on the master node to check the Pods status: Once all the Pods are up and running, you can access the Prometheus console using kubernetes port forwarding. Name the nodes as Kubernetes Master and Kubernetes Worker. Are there tables of wastage rates for different fruit and veg? https://grafana.com/grafana/dashboards/2129. Setting label_limit provides some cardinality protection, but even with just one label name and huge number of values we can see high cardinality. Time arrow with "current position" evolving with overlay number. And this brings us to the definition of cardinality in the context of metrics. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. how have you configured the query which is causing problems? No error message, it is just not showing the data while using the JSON file from that website. Its the chunk responsible for the most recent time range, including the time of our scrape. Especially when dealing with big applications maintained in part by multiple different teams, each exporting some metrics from their part of the stack. @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). Has 90% of ice around Antarctica disappeared in less than a decade? Theres no timestamp anywhere actually. Note that using subqueries unnecessarily is unwise. 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. After running the query, a table will show the current value of each result time series (one table row per output series). Time series scraped from applications are kept in memory. This is in contrast to a metric without any dimensions, which always gets exposed as exactly one present series and is initialized to 0. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. You're probably looking for the absent function. 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. Comparing current data with historical data. By setting this limit on all our Prometheus servers we know that it will never scrape more time series than we have memory for. PromQL tutorial for beginners and humans - Medium Why is there a voltage on my HDMI and coaxial cables? There will be traps and room for mistakes at all stages of this process. I used a Grafana transformation which seems to work. You set up a Kubernetes cluster, installed Prometheus on it ,and ran some queries to check the clusters health. 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? Second rule does the same but only sums time series with status labels equal to "500". By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy.