Zero‑Downtime Deployments on AKS with Azure Application Gateway Ingress Controller (AGIC)

Source: Dev.to | Jan 23, 2026 (UTC)

Background

While deploying applications on Azure Kubernetes Service (AKS) behind Azure Application Gateway Ingress Controller (AGIC), I repeatedly faced brief but noticeable downtime during deployments.

The issue was not with Kubernetes itself, but with how AGIC updates backend pool IPs when pods are replaced during a deployment.

By default, during a rollout:

• Old pods are terminated
• New pods come up with new IPs
• AGIC takes around 30 seconds (sometimes more) to detect and update these new pod IPs in Application Gateway

During this window, Application Gateway may still route traffic to terminating pods → resulting in 5xx errors or downtime.

The Root Cause

Let’s understand what was happening internally:

1. Kubernetes starts terminating old pods
2. Pods are removed from Endpoints
3. AGIC needs time to:

• Detect endpoint changes
• Update Application Gateway backend pool
• Push config updates
  1. Meanwhile, traffic is still flowing

If pods terminate too fast, Application Gateway temporarily has no healthy backend, causing downtime.

The Strategy That Fixed It

After digging into this and testing a few approaches in production, I implemented three small but very effective changes in my Deployment YAML:

1. RollingUpdate Strategy

strategy: type: RollingUpdate rollingUpdate: maxSurge: 1 maxUnavailable: 0

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