After adding one environment variable in values-prod.yaml, production pods lost six others defined in the chart's defaults, including the database host. Helm deep-merges maps but replaces lists entirely. How we spotted it with helm template diffs and restructured values so overrides merge.
Helm 4 is the first major Helm release in six years. We moved forty charts and three deployment pipelines from Helm 3. Notes on what changed for us in practice: server-side apply and field ownership, the new kstatus-based waiting, the plugin system, CLI changes, and the test plan that caught problems before production.
After moving a service to a new Helm chart, every call to it failed with Connection refused while the Pods were Running and Ready. The Service selector no longer matched the Pod labels, and once that was fixed a wrong targetPort kept refusing connections. Here is the debugging path.
We lowered a rate limit in a ConfigMap, Argo CD reported Synced, and the service kept using the old limit for two days. Environment variables from ConfigMaps are read once at container start, and our file mount used subPath, which never updates. A checksum annotation fixed rollouts.
Every deploy of one service failed with another operation is in progress after someone cancelled a pipeline mid-upgrade. The release was stuck in pending-upgrade. We recovered with helm rollback, then added CI concurrency, timeouts and atomic upgrades so it cannot recur.
Half our Argo CD applications showed OutOfSync seconds after every successful sync, and auto-sync kept fighting the HPA over replica counts. The live objects had fields set by controllers and webhooks that Git never mentioned. Targeted ignoreDifferences and server-side diff fixed it.