How Do I Add Custom Headers to HTTP Traffic With Istio EnvoyFilter?

Introduction

In modern cloud environments, managing HTTP traffic efficiently is crucial for security, performance, and compliance. Istio, a popular service mesh, offers advanced traffic management capabilities through its Envoy proxy. One powerful feature of Istio is its ability to customize HTTP traffic by adding custom headers using the EnvoyFilter resource. This can enhance security by including additional metadata, modify existing headers, or integrate with external systems. This guide will walk you through the process of adding custom headers to HTTP traffic using Istio’s EnvoyFilter.

Step-by-Step Explanation

To add custom headers to HTTP traffic using Istio’s EnvoyFilter, follow these steps:

1. Install Istio: Ensure that Istio is installed and properly configured in your Kubernetes cluster. This is a prerequisite for using any Istio features, including EnvoyFilter.

2. Create an EnvoyFilter: Define an EnvoyFilter resource. This resource will specify the custom headers you want to add to the HTTP traffic.

Below is a Pulumi program written in TypeScript that demonstrates how to create an EnvoyFilter to add custom headers to HTTP traffic.

Pulumi Program

import * as pulumi from "@pulumi/pulumi";
import * as k8s from "@pulumi/kubernetes";

// Define the custom headers to be added
const customHeaders = [
    {
        name: "x-custom-header",
        value: "custom-value",
    },
    {
        name: "x-another-header",
        value: "another-value",
    },
];

// Create an EnvoyFilter resource
const envoyFilter = new k8s.apiextensions.CustomResource("custom-headers-filter", {
    apiVersion: "networking.istio.io/v1alpha3",
    kind: "EnvoyFilter",
    metadata: {
        name: "custom-headers-filter",
        namespace: "default",
    },
    spec: {
        workloadSelector: {
            labels: {
                app: "your-app-label", // Apply this filter to workloads with this label
            },
        },
        configPatches: [
            {
                applyTo: "HTTP_FILTER",
                match: {
                    context: "SIDECAR_INBOUND",
                    listener: {
                        filterChain: {
                            filter: {
                                name: "envoy.filters.network.http_connection_manager",
                            },
                        },
                    },
                },
                patch: {
                    operation: "INSERT_BEFORE",
                    value: {
                        name: "envoy.filters.http.lua",
                        typed_config: {
                            "@type": "type.googleapis.com/envoy.extensions.filters.http.lua.v3.Lua",
                            inlineCode: `
                              function envoy_on_request(request_handle)
                                request_handle:headers():add("x-custom-header", "custom-value")
                                request_handle:headers():add("x-another-header", "another-value")
                              end
                            `,
                        },
                    },
                },
            },
        ],
    },
});

// Export the name of the EnvoyFilter
export const envoyFilterName = envoyFilter.metadata.name;

Explanation of the Code

1. Importing Modules: The necessary Pulumi and Kubernetes modules are imported to facilitate the creation of Kubernetes resources.

2. Defining Custom Headers: Custom headers are defined in an array, specifying the name and value of each header to be added to the HTTP traffic.

3. Creating EnvoyFilter: An EnvoyFilter resource is created with the specified configuration.

   • workloadSelector: Specifies the workloads to which this filter should apply. In this example, it applies to workloads with the label app: your-app-label in the default namespace.
   • configPatches: Defines the patches to be applied to the Envoy configuration. The Lua filter is used to add custom headers to inbound HTTP requests.

4. Exporting EnvoyFilter Name: The name of the EnvoyFilter resource is exported for reference, which can be useful for monitoring or debugging.

Key Points

• Istio EnvoyFilter: Allows customization of Envoy proxies in the service mesh, enabling the addition of custom headers.
• WorkloadSelector: Targets specific workloads for the filter application.
• HTTP Filter Configuration: Utilizes Lua scripting to inject custom headers into HTTP requests.

Conclusion

Adding custom headers to HTTP traffic using Istio’s EnvoyFilter is a powerful way to enhance your application’s network traffic management. By following the steps outlined in this guide, you can easily modify HTTP headers to meet your specific needs, whether for security, compliance, or integration purposes. This customization capability is a testament to the flexibility and power of Istio as a service mesh solution.