Microservices and the Web (lecture 4)

A service

Doing something for someone else when requested, here an IT system does something for another IT system on request

RPC

Remote Procedure Call - execute code on another computer connected over a network

API

Application Programming Interface - the things you need to do to call code on another computer

Space coupling (time-coupled)

Communication directed towards a receiver that exists at that moment in time - message passing, remote invocation

Space coupling (time-uncoupled)

Communication directed towards a receiver that can have an independent lifetime

Space uncoupling (time-coupled)

Sender does not need to know receivers identity, but receiver must exist at the point in time

Space uncoupling (time-uncoupled)

Sender does not need to know the identity of the receiver, sender and receiver can have independent lifetimes

Reliability

Tolerating hardware and software faults | Human error

Scalability

Measuring load and performance | Latency percentiles, throughput

Maintainability

Operability, simplicity and evolvability

RPC goal

Transparency through failure masking

HTTP resource

An artifact with state, fx. a document, an image, an airplane booking…

Interaction through CRUD (create, read, update, delete)

HTTP safety

CRUD (create, read, update, delete) is supposed to be idempotent (no additional effect if repeated)

GET and HEAD supposed to have no side-effects

IDL (gRPC)

Interface Definition Language - define messages

Cloud Native

Uses containers, service meshes, microservices, immutable infrastructure to enable loosely coupled systems that are resilient, manageable and observable

Monolithic application

Puts all functionality into single process - scaled by replicating monolith on several servers

Microservices

Puts each element of functionality into a separate service - scaled by distributing services across servers, only replicating when needed

Small, independent, and loosely coupled.

Internal implementation details are hidden.

Microservice philosophy

Service with some philosophy

Business flexibility

Lifecycle - independent changes

High cohesion, low coupling

Microservice downsides

Complexity

Testing

(Lack of) governance

Network load

Data integrity

Versioning

Componentization

Build systems by plugging components together

Products vs projects

Products! Projects end, software stays.

Pipes responsibility

Only transportation, fx. message routing

Synchronous?

Harmful

Time and space decoupled

Multiplies downtime

Implies waiting

You don’t need it!