Ref: https://learn.cantrill.io/courses/1820301/lectures/41301417

• Summary:
• Contents:

Monolith vs DB-split architecture

• Monolith: Web server + application + DB all in one EC2 instance
• DB can be hosted in a different instance or in an AWS-managed DB product (usually latter)
  • DB instance can be in a different AZ
  • ‼️ New dependency: application must communicate with DB in the other instance
    • Extra cost if different AZs (data transit between AZs carries a small cost)
• Monolith (left) vs DB-split architecture (right):
• ❗Single monolithic stacks should be generally avoided! Splitting allows:
  • Independent scaling of different tiers (APP, DB…)
  • Use of different AWS products with associated benefits and optimization

DBs on EC2 are Bad Practice!

• 💡 You should almost always choose an AWS-managed DB product over a DB in EC2

1. 👎 Admin overhead - managing EC2 and DBHost
   • Keeping EC2 instance patched or DBHost compatible with the application is a lot of effort
     • Not trivial to decide whether an update should be done or not
     • Maintenance usually outside of core times, additional effort and stress for staff
   • Added complexity to Backup/DR management
     • Many AWS-managed DB products include automation to remove admin overhead
   • Added complexity to Replication
     • Replication for DBs on EC2 requires skills, setup time, monitoring & effectiveness
     • AWS-managed DB products handle a lot of admin overhead for replication
2. 👎 EC2 is single AZ
   • ‼️ One of the biggest limitations (entails big risk)!
   • If AZ fails → instance fails → DB fails…
     • Mandatory to take EBS snapshots and backups of DB and store them (maybe S3) → extra admin overhead
3. 👎 Lack of features compared to AWS-managed DB products
   • AWS invest time into optimization & features for their DB products
   • E.g.: Performance limit
     • AWS-managed DB products can achieve much higher performance than DB on EC2
   • 💡 Many AWS-managed DB products are truly amazing, and you're missing on many features if you don't use them
4. 👎 No serverless option, no easy scaling
   • EC2 is either ON or OFF
   • EC2 base costs stay the same… DB could be cheaper with other products

Possible Justifications for having a DB in EC2

• Reasons that should be seriously questioned and verified if business really requires them:
  1. Need access to the DB instance OS
     • Not many situations where this is really required though
  2. Advanced DB options tuning that requires DB ROOT level access
     • Many parameters that historically required ROOT level access can nowadays be tuned with AWS products though!
     • Often a vendor demand, not a business demand…
       • Many vendors nowadays support AWS-managed DB products!
• Necessary evil if AWS can't provide a specific DB product:
  1. Run a DB or DB version that AWS don't provide
     • 💡 Very possible, especially with emerging types of DBs, or niche DBs
  2. Very specific OS/DB combination which AWS don't provide
  3. Implement a specific replication/resilience architecture that AWS don't provide