certbot-aws-store

Wrapper tool / function around certbot + route53 that allows to request new certificates, and store them in AWS.

Features

• Store Let's Encrypt certificates in AWS SecretsManager (default) and S3 (optional)
• Keep track of ACME account configuration and store securely in AWS SecretsManager
• Keep track of certificates issued and stored in account via DynamoDB

Pre-Requisites

• A function AWS Account and credentials to make API calls
• Access to DynamoDB + SecretsManager + S3 (optional)

We recommend to create the dynamodb table using the certbot-store-registry.template CFN template, otherwise certbot-aws-store will attempt to create it programmatically.

The needed RCU/WCU should be 5/5 (default) or lower.

Install

pip install certbot-aws-store --user

python3 -m venv venv
source venv/bin/activate
pip install pip -U; pip install certbot-aws-store

Usage

As a CLI

usage: Certbot store wrapper [-h] --secret SECRET --domain DOMAIN --email EMAIL [--register-to-acm] [--dry-run] [--override-folder OVERRIDE_FOLDER] [--profile PROFILE] [--s3-backend-bucket-name BUCKETNAME]
                             [--s3-backend-prefix-key S3_PREFIX_KEY] [--split-secrets] [--secretsmanager-backend-prefix-key SECRETS_PREFIXKEY]

optional arguments:
  -h, --help            show this help message and exit
  --secret SECRET, --secret-store-arn SECRET
                        ACME Configuration secret name/ARN
  --domain DOMAIN       Domain name for the certificate to create
  --email EMAIL         Email for the account and ToS
  --register-to-acm     Creates|Updates certificate in ACM
  --dry-run             By default, use ACME Staging.
  --override-folder OVERRIDE_FOLDER
                        Use an existing certbot folder
  --profile PROFILE     AWS Profile to use for API requests
  --s3-backend-bucket-name BUCKETNAME
                        S3 bucket to store the certificate files into
  --s3-backend-prefix-key S3_PREFIX_KEY
                        S3 Prefix path to store the certificates
  --split-secrets       If set, each certificate file gets their own secret in Secrets Manager
  --secretsmanager-backend-prefix-key SECRETS_PREFIXKEY
                        SecretsManager prefix for secret name

Example

certbot-aws-store --secret dev-acme-store --override-folder certbot-store \
 --email john@ews-network.net \
--domain test-local-0005.bdd-testing.compose-x.io \
--s3-backend-bucket-name dev-test-bucket

Inspiration

Let's Encrypt + Certbot is a goto for anyone who wishes to have free SSL certificates to use in various places. But then the certificates management, storage, backup and so on, still has to be done.

This is an attempt at automating the storage of certificates in AWS and the associated ACME account configuration (to avoid rate limiting).

This tool can be used as a CLI, and coming soon, an AWS Lambda Function or/and (coming soon) a CloudFormation resource. Once installed on AWS, the registry will be automatically looked at daily to identify certificates that need to be renewed and store the new values in appropriate places.

How does it work ?

On the first time, if the ACME secret does not exist, we consider you never used certbot-aws-store before, and a new ACME account will be created, along with the certificate requested.

Once the certificate request is successfully completed, both the certificate and the ACME account details are saved to secrets manager (the certificate)

Using the dynamoDB "registry" table, we store the ARN to the various files stored in AWS, along with some metadata.

For example, the following represents a certificate stored in Secrets Manager, S3 and ACM

{
 "hostname": "test-local-0106.bdd-testing.compose-x.io",
 "account_id": "61811954",
 "acmArn": "arn:aws:acm:eu-west-1:373709667837:certificate/82b3ab6f-5b53-4a3b-ab7d-ccd1ecb52255",
 "endpoint": "acme-staging-v02.api.letsencrypt.org",
 "expiry": "2022-10-20T22:38:59.000000+0000",
 "s3Arn": {
  "certChain": "arn:aws:s3:::dev-test-bucket::certbot/store/acme-staging-v02.api.letsencrypt.org/61812954/test-local-0106.bdd-testing.compose-x.io/chain.pem",
  "fullChain": "arn:aws:s3:::dev-test-bucket::certbot/store/acme-staging-v02.api.letsencrypt.org/61812954/test-local-0106.bdd-testing.compose-x.io/fullchain.pem",
  "privateKey": "arn:aws:s3:::dev-test-bucket::certbot/store/acme-staging-v02.api.letsencrypt.org/61812954/test-local-0106.bdd-testing.compose-x.io/privkey.pem",
  "publicKey": "arn:aws:s3:::dev-test-bucket::certbot/store/acme-staging-v02.api.letsencrypt.org/61812954/test-local-0106.bdd-testing.compose-x.io/cert.pem"
 },
 "secretsmanagerArn": "arn:aws:secretsmanager:eu-west-1:373709667837:secret:certbot/store/acme-staging-v02.api.letsencrypt.org/61812954/test-local-0106.bdd-testing.compose-x.io-HpgyTD",
 "secretsmanagerCertsArn": {}
}

The registry will be used in the future to evaluate / list the certificates that we have and decide whether or not a certificate should be renewed.

When stored in SecretsManager, we might implement a Lambda function to implement the rotation which would update everything, including S3.

Warning

If you use --dry-run to use the ACME staging endpoint for testing, and request the same domain name as for the production ACME endpoint, and store the certificate to ACM, the latest of the two updates the ACM certificate.

Why "bother" ?

With certbot, per account you get 50 certificates requests per week. Which might sound low, but then is even lower when you consider the constraints of other limits.

So of course, considering a world of microservices where you might have 100s of containers needing certificates at the same time, you would breach that limit in no time. So you store them centrally somewhere.

Retrieving the same certificates consistently also will address issues you might have for your clients if you enable features such as HSTS (if you do, allow for rotation within the expiry of the certificates!).