Adding to the answer from Junhwah An:
The certificates generated by ACM aren't retrieved in real-time from the service by the components that are using them (CloudFront, ALB, etc.). Those certificates are loaded when they are generated and then used until they are replaced or expired (if you cancel the automatic renewal).
So a network outage won't affect the certificates being used unless that outage is long enough to block the renewal process.
I'd also add that we don't use the internet for connectivity between regions - we have a private network for that: https://aws.amazon.com/about-aws/global-infrastructure/global_network/
AWS Certificate Manager is a regional service of AWS*.
And the physical and logical separation between AWS Regions avoids correlated failures between them**.
But if you use an ACM certificate for Amazon CloudFront, your certificate has a dependency on the Northern Virginia (us-east-1) region.
Does traffic between Amazon EC2 and Amazon S3 really go over the internet?Accepted Answerasked 3 years ago
Copying EBS Snapshot Across RegionsAccepted Answerasked 2 years ago
Redis Performance Across Different Regionsasked 2 months ago
Sharing application catalog across regionsAccepted Answerasked 10 months ago
Amazon Certificate manager Distribute across regionsasked 4 days ago
Identity Center use across Regionsasked 5 days ago
Does Systems Manager Patch Manager allow patching across multiple accounts and regions?Accepted AnswerMODERATORasked 2 years ago
Amazon RDS for MariaDB instance read replica between regionsasked 3 months ago
Hadoop across multiple regionsasked 3 years ago
List of AMI for a instance type across all regionsAccepted Answerasked 3 years ago