Envoy DNS Resolution Failure

Envoy is unable to resolve the DNS name of the upstream server.

Understanding Envoy Proxy

Envoy is a powerful open-source edge and service proxy designed for cloud-native applications. It is used to manage all incoming and outgoing traffic to services, providing advanced features like load balancing, service discovery, and observability. Envoy is often deployed as a sidecar in service mesh architectures, such as those using Istio.

Identifying DNS Resolution Failures

One common issue encountered with Envoy is DNS resolution failure. This occurs when Envoy cannot resolve the DNS name of an upstream server, leading to connectivity issues. Symptoms include error logs indicating DNS resolution problems and services being unreachable.

Common Error Messages

When DNS resolution fails, you might see error messages in Envoy's logs such as:

upstream connect error or disconnect/reset before headers
DNS resolution failed for host

Exploring the Root Cause

The root cause of DNS resolution failure in Envoy is typically related to incorrect DNS configurations or network issues preventing Envoy from reaching the DNS server. This can happen due to misconfigured DNS settings, network policies blocking DNS traffic, or DNS server outages.

Potential Misconfigurations

Some common misconfigurations include:

Incorrect DNS server IP addresses in Envoy's configuration.
Network policies or firewalls blocking DNS traffic.
DNS server not being reachable from the Envoy instance.

Steps to Resolve DNS Resolution Issues

To resolve DNS resolution failures in Envoy, follow these steps:

1. Verify DNS Configuration

Ensure that the DNS server addresses are correctly configured in Envoy's configuration file. Check the dns_resolvers field in the cluster configuration. For example:

clusters: - name: my_service connect_timeout: 0.25s type: STRICT_DNS dns_resolvers: - socket_address: address: 8.8.8.8 port_value: 53

2. Test DNS Server Reachability

Use tools like dig or nslookup to test if the DNS server is reachable from the Envoy instance:

dig @8.8.8.8 example.com

If the DNS server is not reachable, check network configurations and firewall rules.

3. Check Network Policies

Ensure that network policies or firewalls are not blocking DNS traffic. Review security groups, network ACLs, and firewall rules to allow DNS traffic on port 53.

4. Monitor DNS Server Health

Ensure that the DNS server is operational and not experiencing outages. You can monitor DNS server health using monitoring tools or services.

Further Reading and Resources

For more information on configuring DNS in Envoy, refer to the Envoy Documentation. Additionally, consider exploring Kubernetes DNS if you are running Envoy in a Kubernetes environment.

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