In brief
Exposes system metrics and offer alerts for each ‘droplet’/VM you run.
Data Center Knowledge
Google Cloud Platform
Linux cloud hosting starting at 1GB of RAM for $5/mo. Use promo code WEBOPS20 and get $20 credit.
linode   sponsored 
J.​ Cole Morrison
High Scalability
Paul Tarjan (Stripe)
ELK being Elasticsearch, Logstash and Kibana.
PJ Hagerty
Alex Zirbel
Chang-Hung Liang
See how Rollbar pairs with New Relic to give greater coverage/insights into your application errors. Get x-ray vision into broken code.
ROLLBAR   sponsored 
Uses a YAML-based spec for validating a server’s configuration over time.
Ahmed Elsabbahy
Quickly create and deploy applications that use Amazon API Gateway and AWS Lambda.
Amazon Web Services
Boasts supporting 500K+ requests per second.