All the visualizations are custom D3 / React components.
Lambda powers the monitoring, alerting, and many internal systems such as performing Elasticsearch index garbage collection and maintaining aliases.
All Lambda functions are written in Golang, managed via https://github.com/apex/apex.
Elasticsearch powers both internal logging and the storage for checks and events.
Postgres is used as the primary data store for users, checks, alerts and so on, as well as some aggregated stats.
Firehose stores a backup of all check results to S3.
Historical data archive and backups via Firehose.
SNS forms the connective tissue between most of the Lambda functions.
SES is used for email alert notifications and weekly report summaries.
CloudWatch is used for monitoring Lambda functions and alerting on various internal behaviours.
The apex(1) program is used to manage all of the Lambda functions.