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What is CORS (Cross-Origin Resource Sharing) If you’ve ever worked with APIs in the browser, you probably saw this error: Access to fetch at ‘https://api.example.com/data from origin ‘http://localhost:3000 has been blocked by CORS policy This happens because of CORS — Cross-Origin Resource Sharing. Why CORS Exists Browsers follow the same-origin policy for security. It means that scripts loaded from one origin (domain, protocol, port) cannot freely access resources from another. Otherwise, any website could secretly read your banking data if you’re logged in. ...

What is a CronJob in Kubernetes? If you’ve ever used Linux, you probably know cron – a tool to schedule recurring tasks. Kubernetes has a similar concept called CronJob. A CronJob in Kubernetes is a resource that allows you to run jobs on a schedule, like database backups, sending reports, or periodic cleanup tasks. How CronJobs Work A Job in Kubernetes runs a task once and then exits. A CronJob is a Job with a schedule, defined in cron format (* * * * *). Every time the schedule is triggered, Kubernetes creates a new Job pod. ...

What is MetalLB? If you run Kubernetes in a cloud (AWS, GCP, Azure), creating a LoadBalancer service gives you an external IP automatically. But what if your cluster is bare metal — your own servers, without cloud integration? That’s where MetalLB comes in. MetalLB is a load balancer implementation for bare-metal Kubernetes clusters. It allows you to expose services of type LoadBalancer without relying on cloud providers. How MetalLB Works MetalLB assigns external IPs to services in one of two modes: ...

ETCD ID Mismatch in Kubernetes ETCD is the key-value store used by Kubernetes to keep cluster state. Sometimes you may see the following error in ETCD logs: 2025-11-11 12:13:10.134330 E | rafthttp: request cluster ID mismatch (got fc5dec74b3dcf6fa want 4e38d7b9b94fe83c) It usually happens when a member of the ETCD cluster has a different ID than what the cluster expects. Causes Restoring a backup incorrectly. Copying ETCD data directories between nodes. Node reinstallation without cleaning old ETCD state. Cluster misconfiguration after scaling or failover. How to Fix Step 1: Identify the problem member ...

What is a Headless Service in Kubernetes? In Kubernetes, a Service is typically used to provide a stable IP address and DNS name for a set of Pods. By default, Kubernetes assigns a ClusterIP to the Service, and traffic is load balanced between available Pods. But sometimes you don’t want load balancing — you want direct DNS records for each Pod. That’s where a Headless Service comes in. How It Works A Headless Service is created by setting: ...