You may have legacy applications that expect to consume certain information from files on disk, or from some known environment variable. The resourceFieldRef selector exposes information about an individual container into the container itself. For a list of trademarks of The Linux Foundation, please see our Trademark Usage page. Now lets move on to some richer examples, since one of the things thats most interesting about the Downward API is rich context for observability. Various kinds of status information also can be exposed. Heres a simple example of what it looks like to use the Downward API to expose the rich context that is, the metadata via files. Catch up on part 1. The end result will be a podinfo volume mounted at the path /etc/podinfo, with two files: Alternatively, heres a simple example of how to use the downward API to populate an environment variable value. Swiss Miss is made with fresh milk from local farms, blended with premium imported cocoa! Metadata is labels and annotations. The Kubernetes API reference docs include the Pod API under Workload APIs. There are two different selectors that can be used in the Downward API: the fieldRef selector and the resourceFieldRef selector. With Kubernetes, you have all the tools you need to expose that very same information, dynamically, into running containers. More info. See ingredients, nutrition, and other product information here. If you are missing any of this context, and find yourself often running these kubectl log commands, know that you can get it all via the Pod API. Delicious Swiss Miss hot cocoa mix with marshmallows. Heres another simple demo a live running container that was provisioned via the config file we just showed. It can give you information such as the source of an image; the command you started with; which networking configuration has been applied to an individual container; execution environment variables; resource requirements; and more. In the first part of this series, I discussed the role of observability in the cloud-native journey, and how critical it is when performing any operation. Expose Kubernetes labels or annotations or other metadata about the operating environment to your observability tools, so that all events produced from that pod can have this rich context. Some observability tools try to read directly from the Kubernetes APIs. I find this one interesting because its using a different set of interfaces than we typically think of in the context of a modern API: files and environment variables (instead RESTful HTTP JSON APIs). In this example Im volume mounting files inside of a container using the Downward API. Linux is a registered trademark of Linus Torvalds. The fieldref selector exposes most of the fields from the actual pod resource itself into a container. Find out how we use cookies and how to change your settings. The available fields in the fieldRef are the same three things that we have for managing our resources: metadata, spec, and status. I can specify parameters to determine how much history I want to see, such as how many log lines to display, or how many seconds worth of logs. Expose the node name the underlying kubelet node that the container is running in as an environment variable. Pods are typically created and managed via controllers. Enroll your company as a CNCF End User and save more than $10K in training and conference costs. Guest post by Caleb Hailey, CEO at Sensu. In the first part of this series, I discussed the role of observability in the cloud-native journey, and how critical it is when performing any operation. Configure your observability tooling, like. By submitting this form, you acknowledge that your information is subject to The Linux Foundation's Privacy Policy. Subscribe for updates, event info, webinars, and the latest community news. This is an alternative way to expose richer information to those applications and your monitoring and observability tools. Some of the API endpoints have whats called miscellaneous functions, and the pod API has a very interesting miscellaneous function: to read the logs of any pods containers. 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Leveraging these APIs to fill gaps in your observability is a chance to learn something new. The Downward API makes it easy to access a lot of rich context no matter what observability tools youre using. Spec is things like the service account, or which underlying kubelet node this particular container is running on. This series is adapted from Sensu's whitepaper on the top 7 APIs for cloud-native observability.Catch up on part 1.. Buy Now. Catch up on the latest happenings and technical insights from #TeamCloudNative, Media releases and official CNCF announcements, CNCF projects and #TeamCloudNative in the media, Read transparent, in-depth reports on our organization, events, and projects, Cloud Native Network Function Certification (Beta), Container Security: what it is and how to implement it, Murre the lightweight K8s metrics monitoring tool, Expose pod information via files or environment variables, Useful with monitoring & observability tools, /etc/podinfo/labels a flat file containing all of the pod labels (in key=value format), /etc/podinfo/annotations a flat file containing all of the pod annotations (in key=value format). This website uses cookies to offer you a better browsing experience. This is one of the more well-known commands in the Kubernetes CLI tool. This is tremendously useful for exposing dynamic values to modern and/or legacy tools at predefined environment variables; e.g., if your observability tool expects an environment variable called $TOOL_SPECIAL_VALUE that should contain some value that we can extract from Kubernetes, the the Downward API is exactly the right tool for the job. All rights reserved. For women: 100 calories (25 grams, 6 tsp per day) For men: 150 calories (37 grams, 9 tsp per day) The FDA is more "generous", the Daily Value for added sugars is 200 calories (50 grams, 12 tsp per day). This series is adapted from Sensus whitepaper on the top 7 APIs for cloud-native observability. A better option would be to use the Pods name as an identifier, and inject the Pods name into the well-known environment variable. Like all the other primary, first-class resources in Kubernetes, this API gives you metadata, spec, and status information. See ingredients, nutrition, and other product information here. That could be context such as the CPU and memory requests, and/or limits for the container; you can expose these directly into the container using the Downward API. As you go through the Kubernetes API reference docs, youll notice that every API endpoint supports your normal CRUD operations create, read, update, and delete. In this post, Ill discuss the Kubernetes Pod and Downward APIs. In this demo you can see a couple of example environment variables, and the /etc/podinfo mount path is a directory containing one file for each of the field lists the labels file and of the annotations file. An example is an existing application that assumes a particular well-known environment variable holds a unique identifier. The Kubernetes Downward API enables pods to expose information about themselves to containers running in the pod via files or environment variables. Milk Chocolate with Marshmallow | Swiss Miss Browse all our products and recipe ideas today. Accessibility Statement In this example Im exposing the namespace the pod is running in as an environment variable called $APP_NAMESPACE inside the container. Privacy Policy and Terms of Use. Swiss Miss Hot Chocolate, Marshmallow - fooducate.com I also laid the groundwork for what Ive determined to be the top APIs for cloud-native observability, starting with the Kubernetes metrics, service, and container APIs. Expose Pod Information to Containers Through Environment - Kubernetes Explore cloud native concepts in clear and simple language no technical knowledge required! One interesting fact about Pods is that they are the core building block of all Kubernetes workloads, but it is unlikely that you will ever manage or configure them directly. The most common workflows create Kubernetes StatefulSets, DaemonSets, Deployments, or Jobs; these controllers then create and manage one or more ReplicaSets, and ReplicaSets create and manage the actual pods. I didnt specifically ask for that Kubernetes made that decision for me but having that context make its way into our observations (e.g., the events produced by Sensu) is really valuable for observability, especially when troubleshooting issues in a production context. In Kubernetes, there are two ways to expose Pod and container fields to a running container: Environment variables, as explained in this task Volume files Together . Using files and environment variables provides access to a lot of rich context that can be exposed in backwards-compatible ways for legacy applications. In your controller manifest whether thats a Deployment or StatefulSet or DaemonSet you configure volume mounts or environment variables that read their contents or values from the downward API. In the third and final part of this series, Ill discuss the Kubernetes Events API and API Watchers. Delicious Hot Cocoa & Hot Chocolate | Swiss Miss The Downward API is actually a pod configuration directive. The top Kubernetes APIs for cloud-native observability, part 2: the Swiss Miss Marshmallow Lovers has separate envelopes with 4.5 times the marshmallows of regular Swiss Miss hot cocoa mix with marshmallows. This page shows how a Pod can use environment variables to expose information about itself to containers running in the Pod, using the downward API. Marshmallow Lovers | Swiss Miss The Linux Foundation has registered trademarks and uses trademarks. This last screenshot is particularly interesting because its a simple Deployment with three replicas, and when Kubernetes scheduled the Pods it ended up running one on each of my three Kubelets. One possibility is to wrap the application, but that is tedious and error prone, and it violates the goal of loose coupling. You can use environment variables to expose Pod fields, container fields, or both. The Kubernetes reference documentation emphasizes the importance of gathering information about containers without coupling too tightly with Kubernetes: It is sometimes useful for a Container to have information about itself, without being overly coupled to Kubernetes. The Downward API is one of the more interesting Kubernetes APIs because of the importance of high-cardinality in observability structured events with highly variable values make for rich observations. Thats useful in case you need to correlate issues impacting multiple containers are they all running on the same node? Here at Fooducate, we suggest sticking to the stricter option (only 25 grams per day for women, 37 grams for men). If youve used the kubectl log command, you can get the very same output programmatically from the Kubernetes APIs. I can request the logs for this particular pod, and for a specific container member of the pod. Regardless if youre a Kubernetes expert or just getting started with Kubernetes, you have almost certainly run the command kubernetes describe pod
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