istio-check

An example of an iptables rule manipulated by Istio's Envoy proxy setup involves redirecting incoming and outgoing traffic to the Envoy sidecar proxy. Below is a simplified representation of how Istio might set up iptables rules to intercept traffic:

1. Redirect Incoming Traffic to Envoy: This rule redirects incoming traffic on the pod to the Envoy proxy, which listens on a specific port (e.g., 15001). All incoming traffic to the pod is intercepted and passed through the Envoy proxy for management before reaching the application container.

iptables -t nat -A PREROUTING -p tcp -j REDIRECT --to-port 15001

# Delete
sudo iptables -t nat -D PREROUTING -p tcp --anywhere --anywhere -j REDIRECT --to-ports 15001

1. Redirect Outgoing Traffic to Envoy: Similar to incoming traffic, this rule intercepts outgoing traffic from the pod and redirects it to the Envoy proxy. This allows the proxy to apply routing rules, load balancing, and security policies before the traffic leaves the pod.

iptables -t nat -A OUTPUT -p tcp -j REDIRECT --to-ports 15001

1. Exclude Envoy's Traffic from Being Intercepted: To prevent loops where Envoy's traffic is intercepted by its own rules, traffic originating from the Envoy proxy itself can be excluded from redirection.

iptables -t nat -A OUTPUT -p tcp -d 127.0.0.1/32 --dport 15001 -j RETURN

1. Management and Health Checks: Istio might also configure iptables to allow direct traffic for management and health checks, avoiding the Envoy proxy for specific endpoints or ports.

iptables -t nat -A OUTPUT -p tcp --dport 15020 -j RETURN

These commands collectively ensure that all traffic entering and leaving the pod is intercepted by the Envoy proxy, except for the proxy's own traffic and specific exclusions for management and health checks. This setup enables the rich feature set of Istio's service mesh, including security features, observability, and traffic control, without requiring any changes to the applications themselves.

Note: The actual iptables rules and ports used by Istio can vary based on the configuration and version of Istio. This example is intended to illustrate the concept rather than provide a ready-to-use script.