Six skills one should develop to grow into senior+ SWE positions.

1. Data modelling
   • entity: a concept or object in real world that can be uniquely identified (ex: person, place), represented by a table in db
   • attribute: characteristics of entity (ex: name, age), represented by a column in db
   • relationship: how entities are related to each other (ex: person has a name), can be 1-1, 1-many, many-many.
2. Events, Message Queues, and Workers
   • distributed systems that process work in real time (APIs) and asynchronously (queues + workers)
   • one key piece of asynchronous systems is message queues, which are used to:
     • rate limit processing of events
     • communicate between microservices
     • shard load of specific types of events to be processed at different rates
     • batch process a bunch of events
   • ex: instead of one mega server handing all tasks, throw them on a queue, have worker pods scale and pick them up, and send them asynchronously
   • also used for interservice communication
3. Autoscaling infrastructure
   • for monoliths: setup autoscaling ec2
   • for microservices: implement horizontal pod autoscaling in k8s
   • db: amazon aurora spins up new replicas based on increase load
4. Cloud Technologies
   • can't avoid learning, need real-world experience solving business scaling problems
   • ex in AWS
     • SNS, SQS : message queues
     • S3 : storage
     • kafka, kinesis: event streaming
     • EC2: monoliths
5. Caching
   • caching allows system to handle more load, respond faster, without scaling up
   • read engineering blogs and system design to understand where/when to apply caching, instead of just saying "throw redis at it"
   • types of caching:
     • site cache: serve content quickly to return users
     • application/output cache: server level HTML caching
     • distributed data cache: redis, memcached
     • file caching: CDN for static files
6. Concurrency / Idempotency
   • idempotency = ability to execute same operation multiple times without changing the result beyond the initial application
     • ex: customer submitting same order multiple times (because of bugs) -> only one order is created
     • how? send an idempotency key via api request, where it could be a hashed key of the forms data