Maintaining Transport Layer Security All the Way to Your Container, Part 2: Utilizing AWS Certificate Manager Private Certificate Authority

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In this installment, we delve into the various strategies for ensuring that certificates can be securely and reliably accessed by containers. By streamlining the generation and distribution of certificates and other sensitive materials, you can develop inherently secure architectures without sacrificing scalability.

There are several approaches to achieve this:

1. Embedding the Certificate and Private Key in the Docker Image
   Certificates and keys can be embedded within the Docker image and accessed by the container during runtime. This method simplifies container deployment with certificates and keys. However, it has significant drawbacks. Firstly, certificates and keys must be created, stored securely, and incorporated into the Docker image. This requires manual or additional automation steps to securely manage them for every new Docker image revision.

   The following Dockerfile illustrates how to create an NGINX container that includes the certificate and the key:

   FROM nginx:alpine
   
   # Copy in secret materials
   RUN mkdir -p /root/certs/nginxdemotls.com
   COPY nginxdemotls.com.key /root/certs/nginxdemotls.com/nginxdemotls.com.key
   COPY nginxdemotls.com.crt /root/certs/nginxdemotls.com/nginxdemotls.com.crt
   RUN chmod 400 /root/certs/nginxdemotls.com/nginxdemotls.com.key
   
   # Copy in nginx configuration files
   COPY nginx.conf /etc/nginx/nginx.conf
   COPY nginxdemo.conf /etc/nginx/conf.d
   COPY nginxdemotls.conf /etc/nginx/conf.d
   
   # Create folders to hold web content and copy in HTML files.
   RUN mkdir -p /var/www/nginxdemo.com
   RUN mkdir -p /var/www/nginxdemotls.com
   
   COPY index.html /var/www/nginxdemo.com/index.html
   COPY indextls.html /var/www/nginxdemotls.com/index.html
       

   However, this approach also raises security concerns, as anyone with access to the Docker image can retrieve the embedded certificate and private key. Additionally, updated certificates must be manually replaced, necessitating the recreation of the Docker image.

2. Utilizing AWS Systems Manager Parameter Store and Amazon S3
   The post Managing Secrets for Amazon ECS Applications Using Parameter Store and IAM Roles for Tasks details how to leverage Systems Manager Parameter Store for secret management. Some users opt for Parameter Store for its ease of retrieval and fine-grained access control. It allows securing data with AWS Key Management Service (AWS KMS) encryption. Each KMS key can be accessed and managed using AWS Identity and Access Management (IAM) roles, providing resource-level permissions.

   Certificates can be stored in Parameter Store as ‘Secure String’ types and encrypted with KMS. This allows an API call to retrieve the certificate during container deployment. This method permits certificate replacement without needing to update the Docker image. For more details, check out this another blog post.

   However, Parameter Store has a 4,096 character limitation, which may not accommodate all certificate types. In such cases, Amazon S3 can be used to store longer certificates while using Parameter Store for sensitive data like private keys or passwords.

3. Employing AWS Secrets Manager
   AWS Secrets Manager provides robust features for managing credentials, keys, and other sensitive materials, allowing for dynamic referencing without embedding them in application code. This service enables fine-grained access control through IAM policies and offers features for revocation and rotation through API calls.

   All stored materials are encrypted with a KMS key of your choice. AWS Secrets Manager has a similar character limitation of 4,096 characters, which may necessitate storing certificates and keys in separate secrets. Secrets are retrievable by container instances at runtime through the AWS Command Line Interface (AWS CLI) or application code, provided the container task role has the necessary IAM permissions.

   For additional insights, this resource is an excellent source.

4. Creating Self-Signed Certificates During Docker Container Creation
   This approach allows for TLS communications without the complexities of distributing certificates. However, it requires implicit trust of the server, which may trigger warnings regarding the lack of an acceptable root of trust.
5. Building and Managing a Private Certificate Authority
   A private certificate authority (CA) offers enhanced security and flexibility compared to previous solutions. Typically, a private CA will manage:
   • A private key
   • A certificate issued with the private key
   • Lists of issued and revoked certificates
   • Policies governing certificate requests
   • Audit logs for tracking

   For further authoritative insights on this topic, refer to this link.

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