AWS Certificate Manager (ACM) Importing Public Certificates | Deep Dive.

A deep dive into AWS Certificate Manager (ACM)  Importing Public Certificates.

Focus:

•        Overview of the Importation process for a Public Certificate,
•        Architecture: How Imported Certificates Work,
•        Required Files for Import,
•        Importing via AWS CLI,
•        CloudFormation Sample,
•        Cross-Region and Cross-Account Usage,
•        Security and Key Management,
•        Integration with AWS Services,
•        Automation and Lifecycle Management,
•        Best Practices.

1. Overview of the Importation process for a Public Certificate.

•        ACM can automatically issue and renew public certificates through Amazon Trust Services.
•        However, twtech might need to import an existing certificate into AWS.

Use Case	Example
External CA	Certificate issued by DigiCert, Let’s Encrypt, Entrust, etc.
Custom trust chain	Enterprise PKI or hybrid cloud environment
Key export control	twtech generated private keys and want full control
Pre-existing certs	Migrating workloads already using external certs

 Key Difference:
When importing, twtech manages renewal and re-import — ACM does not automatically renew imported certificates.

 2. Architecture: How Imported Certificates Work

Here’s a breakdown of the imported certificate architecture inside ACM:

Architecture Components

Component	Description
AWS Certificate Manager (ACM)	Stores and deploys the imported certificate.
External Certificate Authority (CA)	Issues the certificate and provides the cert chain.
Private Key Owner	twtech (the user) generates and hold the private key.
Target Services	ALB, CloudFront, API Gateway, etc. consuming the cert.

Import Flow

 3. Required Files for Import

NB:

When twtech import a certificate into ACM, it needs three components:

File	Description
Certificate Body	The public cert file (.crt) issued by the CA.
Certificate Chain	Intermediate CA(s) up to the root CA.
Private Key	The private key (.key) corresponding to the cert.

NB:

All must be PEM-encoded and unencrypted.

Example:

-----BEGIN CERTIFICATE-----

<twtech certificate body>

-----END CERTIFICATE-----

-----BEGIN CERTIFICATE-----

<intermediate certificate>

-----END CERTIFICATE-----

 4. Importing via AWS CLI

# bash

aws acm import-certificate \

  --certificate fileb://twtechcertificate.pem \

  --private-key fileb://twtechprivate-key.pem \

  --certificate-chain fileb://twtechcertificate-chain.pem \

  --tags Key=Environment,Value=twtechProd

• ACM returns a Certificate ARN, which twtech can then attach to ALBs, CloudFront distributions, etc.
• The private key cannot be encrypted with a password — remove passphrases before import.

 5. CloudFormation Sample

# yaml

Resources:

  ImportedCertificate:

    Type: AWS::CertificateManager::Certificate

    Properties:

      CertificateBody: |

        -----BEGIN CERTIFICATE-----

        MIIF...

        -----END CERTIFICATE-----

      PrivateKey: |

        -----BEGIN RSA PRIVATE KEY-----

        MIIE...

        -----END RSA PRIVATE KEY-----

      CertificateChain: |

        -----BEGIN CERTIFICATE-----

        MIIE...

        -----END CERTIFICATE-----

NB:

 CloudFormation doesn’t directly support automatic renewal or referencing S3 secrets — twtech must manually update the stack to rotate certificates.

 6. Cross-Region and Cross-Account Usage

ACM certificates are regional, even when imported.

To use across Regions:

• Import the same certificate in each target Region.
• twtech can automate this via AWS Lambda or CI/CD pipelines to replicate certs to multiple Regions.

To use across Accounts:

• Use Resource Sharing via AWS RAM for ALB/NLB certificates.
• Or deploy a copy in each account using CloudFormation StackSets.

 7. Security and Key Management

Area	Description
Private Key Storage	Encrypted at rest by ACM using AWS KMS (twtech can’t access it after import).
Access Control	IAM policies control who can import, view, or delete certs.
Audit Trail	All actions logged via CloudTrail (e.g., ImportCertificate, DeleteCertificate).
No Export	Imported private keys cannot be exported once uploaded.
Rotation Policy	twtech must manually re-import when the cert is renewed externally.

 8. Integration with AWS Services

AWS Service	Integration Details
ALB / NLB	Use the certificate ARN in the HTTPS listener.
CloudFront	Must import the cert in us-east-1 (N. Virginia).
API Gateway	Attach via custom domain configuration.
Elastic Beanstalk	Specify certificate ARN in environment config.

 9. Automation and Lifecycle Management

A. Pipeline-based Automation (Sample Workflow)

B. Renewal Workflow

1. Detect expiring cert (e.g., via EventBridge or cron).
2. Request a new one from twtech CA.
3. Import into ACM.
4. Update dependent resources.

10. Best Practices

Category	Best Practice
Key Generation	Generate keys using strong algorithms (RSA 2048+, ECC).
Automation	Automate imports and rotations using Lambda or CI/CD.
Security	Never store unencrypted private keys in source control.
Region	Always import to us-east-1 for CloudFront distributions.
Monitoring	Use EventBridge + CloudWatch to detect expiring certs.
Tagging	Tag imported certs with environment and ownership metadata.

 11. Sample Architecture – Automated Import & Rotation