Kubernetes is a highly expandable framework made up of loosely linked components. This provides a great amount of flexibility but introduces some new operational issues as compared to previous monolithic solutions for similar systems.
This modularity provides a great deal of flexibility but also creates new operational issues. One of the challenges Kubernetes users face is observability. In this article, we'll review the different Kubernetes events log collection methods and interfaces for Kubernetes components.
In a Kubernetes cluster, the most commonly utilised components and events are:
The Kubernetes API server serves as the single point of contact for all core components, including extensions such as operators. Its primary responsibilities include authenticating and authorising requests, providing audit information, validating incoming objects and if required, mutating them, and persisting state in etcd.
In a high availability scenario, there is more than one API server, and because all API servers normally accept requests, all of them output logs at the same time.
The API server logs can be useful for learning more about unsuccessful API queries, but they are usually irrelevant. When the API server fails, the API server logs are required for infrastructure operations.
Etcd is a key part of the Kubernetes architecture. It is only utilised by the API server and hence isn't interesting until it stops performing as planned. Long-term historic logs may also be beneficial in this scenario for infrastructure operations engineers to determine whether specific occurrences occurred previously or to track out the intricacies and fundamental causes of a disaster.
Those who run a self-managed Kubernetes cluster may need to access etcd logs if their nodes encounter issues. In most cases, etcd runs outside the Kubernetes cluster on the master hosts, making methods for collecting logs fairly similar to those used with logs from API servers. Cloud providers' managed Kubernetes products do not provide access to etcd logs, but infrastructure operations may require them in the event of self-managed clusters.
Kubernetes can run without an authenticator, but it also serves as a strong integration point for other authentication providers. The authenticator is a distinct control plane component in the majority of managed Kubernetes services that uses credentials for certain providers given by external clients for validation and gives the information required by use of the API Server for approval.
It should be noted that the authenticator is often used to validate external components or users instead of services within a cluster.
Authenticator logs are often accessible exclusively through the cloud provider's log stack. It may just be necessary to configure log collection. If the authenticator is operated independently, any cloud logging operator may gather its standard outputs.
Authenticator logs are useful for either security or infrastructure operations teams during an incident examination or troubleshooting.
Kubernetes controllers are things that watch the state of the cluster and try to move it towards what they think is the intended state. One of these controllers is called the controller manager, which embeds all the principal control loops that ship with Kubernetes.
In Kubernetes, a control loop is a loop that never ends and controls how a system works. A controller manager is a control loop that keeps an eye on the shared state of the cluster through the API server and makes changes to move the current state closer to the desired state. Example controllers are:
Its logs are useful in reconstructing the sequence of events during an incident investigation or analysing the system's behaviour. These logs are necessary for effectively running infrastructure, cloud-native apps, and investigating security incidents.
It is the component of Kubernetes responsible for assigning Pods to Nodes. It assesses, based on constraints and available resources, which Nodes are genuine placements for each Pod. It then ranks each valid Node and allocates the Pod to one of them. A cluster can have multiple schedulers; the reference implementation is a Kube scheduler.
Only the leader scheduler generates logs in a high-availability system. This is true even if one is using custom schedulers in the cluster for whatever reason.
If one is having trouble with containers not starting or if they are getting errors about them, the best way to troubleshoot is with the help of Kubelet logs. Kubelet is a cluster agent that runs on every node in the cluster. One can use one of the following methods to register the node with the API server:
The hostname is baked into the image and cannot be modified by users or admins. It is recommended to use this option unless there is a good reason not to.
A flag to override the hostname, which allows one to specify a custom name for the node when it registers with Kubernetes. This requires specifying --hostname [hostname] at startup time as an argument to the script or in the system.
Specific logic for a cloud provider, which allows one to customise how their node registers itself with Kubernetes by specific requirements for that cloud provider.
To manage the network traffic in Kubernetes, a network proxy operates on each node and is in charge of maintaining the cluster IPs and ports utilised by services. This represents Kubernetes API-defined services on each node and can perform simple stream forwarding or round-robin forwarding across a set of backends. An optional add-on is available that provides cluster DNS for these cluster IPs. To configure the proxy, the user needs first to create a service using the API server.
This post focused on discussing the most significant components of a Kubernetes cluster output log messages and how to retrieve them in various scenarios.
While the operator works on almost every possible Kubernetes distribution, architecture, or deployment, collecting logs from Kubernetes components located outside of the cluster may require significant effort. Candidates interested in DevOps training can enrol in the DevOps certification course by visiting the StarAgile website.
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