Securing east-west traffic in service meshes, such as AWS App Mesh, by using mutual Transport Layer Security (mTLS) adds an additional layer of defense beyond perimeter control. mTLS adds bidirectional peer-to-peer authentication on top of the one-way authentication in normal TLS. This is done by adding a client-side certificate during the TLS handshake, through which a client proves possession of the corresponding private key to the server, and as a result the server trusts the client. This prevents an arbitrary client from connecting to an App Mesh service, because the client wouldn’t possess a valid certificate.

In this blog post, you’ll learn how to enable mTLS in App Mesh by using certificates derived from AWS Certificate Manager Private Certificate Authority (ACM Private CA). You’ll also learn how to reuse AWS CloudFormation templates, which we make available through a companion open-source project, for configuring App Mesh and ACM Private CA.

You’ll first see how to derive server-side certificates from ACM Private CA into App Mesh internally by using the native integration between the two services. You’ll then see a method and code for installing client-side certificates issued from ACM Private CA into App Mesh; this method is needed because client-side certificates aren’t integrated natively.

You’ll learn how to use AWS Lambda to export a client-side certificate from ACM Private CA and store it in AWS Secrets Manager. You’ll then see Envoy proxies in App Mesh retrieve the certificate from Secrets Manager and use it in an mTLS handshake. The solution is designed to ensure confidentiality of the private key of a client-side certificate, in transit and at rest, as it moves from ACM to Envoy.

The solution described in this blog post simplifies and allows you to automate the configuration and operations of mTLS-enabled App Mesh deployments, because all of the certificates are derived from a single managed private public key infrastructure (PKI) service—ACM Private CA—eliminating the need to run your own private PKI. The solution uses Amazon Elastic Container Services (Amazon ECS) with AWS Fargate as the App Mesh hosting environment, although the design presented here can be applied to any compute environment that is supported by App Mesh.

Solution overview

ACM Private CA provides a highly available managed private PKI service that enables creation of private CA hierarchies—including root and subordinate CAs—without the investment and maintenance costs of operating your own private PKI service. The service allows you to choose among several CA key algorithms and key sizes and makes it easier for you to export and deploy private certificates anywhere by using API-based automation.

App Mesh is a service mesh that provides application-level networking across multiple types of compute infrastructure. It standardizes how your microservices communicate, giving you end-to-end visibility and helping to ensure transport security and high availability for your applications. In order to communicate securely between mesh endpoints, App Mesh directs the Envoy proxy instances that are running within the mesh to use one-way or mutual TLS.

TLS provides authentication, privacy, and data integrity between two communicating endpoints. The authentication in TLS communications is governed by the PKI system. The PKI system allows certificate authorities to issue certificates that are used by clients and servers to prove their identity. The authentication process in TLS happens by exchanging certificates via the TLS handshake protocol. By default, the TLS handshake protocol proves the identity of the server to the client by using X.509 certificates, while the authentication of the client to the server is left to the application layer. This is called one-way TLS. TLS also supports two-way authentication through mTLS. In mTLS, in addition to the one-way TLS server authentication with a certificate, a client presents its certificate and proves possession of the corresponding private key to a server during the TLS handshake.

Example application

The following sections describe one-way and mutual TLS integrations between App Mesh and ACM Private CA in the context of an example application. This example application exposes an API to external clients that returns a text string name of a color—for example, “yellow”. It’s an extension of the Color App that’s used to demonstrate several existing App Mesh examples.

The example application is comprised of two services running in App Mesh—ColorGateway and ColorTeller. An external client request enters the mesh through the ColorGateway service and is proxied to the ColorTeller service. The ColorTeller service responds back to the ColorGateway service with the name of a color. The ColorGateway service proxies the response to the external client. Figure 1 shows the basic design of the application.

The two services are mapped onto the following constructs in App Mesh:

• • ColorGateway is mapped as a Virtual gateway. A virtual gateway in App Mesh allows resources that are outside of a mesh to communicate to resources that are inside the mesh. A virtual gateway represents Envoy deployed by itself. In this example, the virtual gateway represents an Envoy proxy that is running as an Amazon ECS service. This Envoy proxy instance acts as a TLS client, since it initiates TLS connections to the Envoy proxy that is running in the ColorTeller service.

• • ColorTeller is mapped as a Virtual node. A virtual node in App Mesh acts as a logical pointer to a particular task group. In this example, the virtual node—ColorTeller—runs as another Amazon ECS service. The service runs two tasks—an Envoy proxy instance and a ColorTeller application instance. The Envoy proxy instance acts as a TLS server, receiving inbound TLS connections from ColorGateway.

Let’s review running the example application in one-way TLS mode. Although optional, starting with one-way TLS allows you to compare the two methods and establish how to look at certain Envoy proxy statistics to distinguish and verify one-way TLS versus mTLS connections.

For practice, you can deploy the example application project in your own AWS account and perform the steps described in your own test environment.

Note: In both the one-way TLS and mTLS descriptions in the following sections, we’re using a flat certificate hierarchy for demonstration purposes. The root CAs are issuing end-entity certificates. The AWS ACM Private CA best practices recommend that root CAs should only be used to issue certificates for intermediate CAs. When intermediate CAs are involved, your certificate chain has multiple certificates concatenated in it, but the mechanisms are the same as those described here.

One-way TLS in App Mesh using ACM Private CA

Because this is a one-way TLS authentication scenario, you need only one Private CA—ColorTeller—and issue one end-entity certificate from it that’s used as the server-side certificate for the ColorTeller virtual node.

Figure 2, following, shows the architecture for this setup, including notations and color codes for certificates and a step-by-step process that shows how the system is configured and functions. Because this architecture uses a server-side certificate only, you use the native integration between App Mesh and ACM Private CA and don’t need an external mechanism for certificate integration.

The steps in Figure 2 are:

Step 1: A Private CA instance—ColorTeller—is created in ACM Private CA. Next, an end-entity certificate is created and signed by the CA. This certificate is used as the server-side certificate in ColorTeller.

Step 2: The CloudFormation templates configure the ColorGateway to validate server certificates against the ColorTeller private CA certificate chain. As the App Mesh endpoints are starting up, the ColorTeller CA certificate trust chain is ingested into the ColorGateway Envoy instance. The TLS configuration for ColorGateway in App Mesh is shown in Figure 3.

Figure 3 shows that the client policy attributes for outbound transport connections for ColorGateway have been configured as follows:

• • Enforce TLS is set to Enforced. This enforces use of TLS while communicating with backends.

• • TLS validation method is set to AWS Certificate Manager Private Certificate Authority (ACM-PCA hosting). This instructs App Mesh to derive the certificate trust chain from ACM PCA.

• • Certificate is set to the Amazon Resource Name (ARN) of the ColorTeller Private CA, which is the identifier of the certificate trust chain in ACM PCA.

This configuration ensures that ColorGateway makes outbound TLS-only connections towards ColorTeller, extracts the CA trust chain from ACM-PCA, and validates the server certificate presented by the ColorTeller virtual node against the configured CA ARN.

Step 3: The CloudFormation templates configure the ColorTeller virtual node with the ColorTeller end-entity certificate ARN in ACM Private CA. While the App Mesh endpoints are started, the ColorTeller end-entity certificate is ingested into the ColorTeller Envoy instance.

The TLS configuration for the ColorTeller virtual node in App Mesh is shown in Figure 4.

Figure 4 shows that various TLS-related attributes are configured as follows:

• • Enable TLS termination is on.

• • Mode is set to Strict to limit connections to TLS only.

• • TLS Certificate method is set to ACM Certificate Manager (ACM) hosting as the source of the end-entity certificate.

• • Certificate is set to ARN of the ColorTeller end-entity certificate.

Note: Figure 4 shows an annotation where the certificate ARN has been superimposed by the cert icon in green color. This icon follows the color convention from Figure 2 and can help you relate how the individual resources are configured to construct the architecture shown in Figure 2. The cert shown (and the associated private key that is not shown) in the diagram is necessary for ColorTeller to run the TLS stack and serve the certificate. The exchange of this material happens over the internal communications between App Mesh and ACM Private CA.

Step 4: The ColorGateway service receives a request from an external client.

Step 5: This step includes multiple sub-steps:

• • The ColorGateway Envoy initiates a one-way TLS handshake towards the ColorTeller Envoy.

• • The ColorTeller Envoy presents its server-side certificate to the ColorGateway Envoy.

• • The ColorGateway Envoy validates the certificate against its configured CA trust chain—the ColorTeller CA trust chain—and the TLS handshake succeeds.

Verifying one-way TLS

To verify that a TLS connection was established and that it is one-way TLS authenticated, run the following command on your bastion host:

$ curl -s http://colorteller.mtls-ec2.svc.cluster.local:9901/stats |grep -E 'ssl.handshake|ssl.no_certificate'

{

$ curl -s http://colorteller.mtls-ec2.svc.cluster.local:9901/stats |grep -E 'ssl.handshake|ssl.no_certificate'