The kubelet runs on each node and consists of several components that work together to ensure containers are properly managed and the node stays in sync with the cluster:

• Kubelet Agent: Acts as the primary node agent, facilitating communication between the node and the Kubernetes control plane. It processes Pod specifications and ensures containers are running as expected.
• Kubelet API Server: Provides an interface for communication with other cluster components and exposes HTTP endpoints used for management and diagnostics.
• Container Runtime Interface (CRI): Integrates with container runtimes like containerd or CRI-O to pull images, start containers, and manage their lifecycle according to the kubelet’s instructions.
• Probes and Health Checks: Performs liveness, readiness, and startup checks on containers to monitor their status and trigger restarts or remediation as needed.
• Volume Manager: Handles mounting and unmounting of storage volumes for pods, ensuring persistent data availability throughout pod lifecycles.

The kubelet architecture is designed to coordinate containerized workloads and synchronize the node with the overall Kubernetes cluster. Here’s how its main components fit together:

• Control Plane Interaction: Maintains an ongoing communication channel with the Kubernetes control plane. This allows the exchange of pod scheduling instructions, status updates, and node health information, keeping the node in sync with the desired cluster state.
• Pod Management Loop: Continuously observes desired pod configurations (PodSpecs) received from the control plane or local manifest files, and works to create, update, or delete containers so that reality matches the specified intent.
• Container Runtime Integration: Links to the container runtime through the Container Runtime Interface (CRI), supplying commands to start, stop, or inspect containers and handle image pulls and updates as needed.
• Monitoring and Reporting Engine: Periodically runs checks—known as probes—on containers and the node, monitoring health, resource usage, and status. It regularly reports these findings back to the control plane for visibility and automated remediation.
• Volume and Storage Coordinator: Manages all aspects of pod storage, including mounting, unmounting, and maintaining access to persistent volumes in line with pod and node lifecycles.
• API and HTTP Endpoints: Exposes secured HTTP(S) interfaces that allow for diagnostics, metrics collection, and administrative operations, accessible by authorized cluster components or administrators.

To ensure smooth pod execution and node operation, the kubelet follows a set of essential operational concepts in every Kubernetes cluster:

• PodSpec Processing: The kubelet listens for Pod specifications from the control plane or specified files and translates them into running containers. Any changes to these specs are detected and acted on in near real-time.
• Desired State Enforcement: Continuously checks the actual state of containers against the desired definitions, taking action to start, stop, or restart containers to maintain consistency with cluster instructions.
• Probing and Health Checking: Regularly runs liveness, readiness, and startup probes to assess whether containers are functioning correctly, are ready to serve traffic, or require remediation.
• Status Reporting: Sends frequent updates about pod status and node health to the control plane. This constant communication supports fast failover and rescheduling if a problem is detected.
• Resource Allocation and Enforcement: Ensures each container receives its requested amounts of CPU, memory, and storage, and enforces quotas or throttles usage when limits are exceeded to keep the node healthy.
• Volume and Storage Management: Mounts, unmounts, and maintains persistent volume access for pods, enabling reliable storage even when pods are restarted or moved.
• Static Pod Handling: Loads and manages static pod definitions from the filesystem, allowing critical cluster components to be started directly by the kubelet even if the control plane is not fully available.
• Security Policy Enforcement: Implements security boundaries, pod isolation, and credentials handling as defined by the cluster’s policies, keeping node and workload environments secure.

Ensuring the health and stability of kubelet operations requires both proactive monitoring and effective troubleshooting. Here are practical steps and habits to keep your nodes running smoothly:

• Investigate Node Status: When a node is reported as NotReady, check kubelet logs and review system resource usage. Common issues include low memory, full disks, or stopped kubelet services.
• Centralize Logs and Metrics: Forward kubelet logs and container metrics to a centralized logging stack for easier searching and correlation. Use dashboards to quickly spot anomalies or trends before they become outages.
• Actively Monitor Resources: Monitor CPU, memory, storage, and network usage on each node. Set alerts to notify your team if any thresholds are breached so you can respond before workloads are impacted.
• Master Core Commands: Become fluent with commands like kubectl describe node, kubectl logs, and kubectl top to quickly gather information when troubleshooting issues.
• Secure the Kubelet: Disable anonymous authentication, use TLS, and restrict API endpoint access. Deploy Role-Based Access Control (RBAC) rules to limit exposure and prevent unauthorized actions.
• Embrace Configuration Files: Use configuration files for kubelet settings rather than relying on command-line flags. This ensures consistency, repeatability, and easier automation across your environment.
• Automate Common Tasks: Script routine health checks, log management, and configuration enforcement to reduce manual effort and minimize human error.
• Establish Regular Review Cycles: Periodically audit node configurations, security posture, and update schedules. Regular maintenance and routine patching help minimize risk and improve reliability.