The sidecar

A sidecar is a one-wheeled device attached to the side of a motorcycle. (Wiki)

Ref: https://youtu.be/WH-Cnd88yO4

The sidecar pattern in Microservices

Advantages

• Keep application logic intact and maintainable

  • Carry on extra trivial tasks

  • Simplify the complexity of service design

• ​Secure or access control of the application service

  • Network traffic filtering

  • Protocol transfer

    • e.g. Redis's in-transit encryption

• Reusability of components​

  • ​Common logic is reusable across similar application services

• ​Explicit service boundary

  • ​Programming language separating

Use cases 

• Adapt legacy applications

• Modularity and reuse of the components

• Configuration synchronization

• Automatic service update

• TLS/SSL termination
  • Circuit breaking, routing, and monitoring
• ​Log collector
• Proxy and caching

Sidecar Example 1

Adding HTTPS to a legacy service

Sidecar Example 2

Configuration synchronization

Camera config caching service

Case study in Umbo CV

There are too many RESTful API calls querying camera configurations from our CV pipeline and video streaming services ......

• Actually, camera info would not be changed frequently.

• But, we still want our services to get updates asap. 

CornerBear is born

CornerBear is a sidecar caching service for Media Server and CV Router aims to help them manage cameras' info and notify changes for registered events.

Even a sidecar, we still need to design its architecture strictly.

Service log collector

Case study in Umbo CV

Network is unreliable

You have no idea what a network request may meet during its journey.

If services fail to log, should they handle errors by themselves?

e.g. Retry sending, message buffering ...etc

Sidecar for log collection

• Apply Fluentd as a sidecar logger collector.
• Event-based, interval flushing, and autonomy.

To be successful, a sidecar should be simple but flexible.

• Parameterizing your services

  • ​Configure them through environment variables or CLI

• Define the compatible API surface

  • ​In microservices, API is the only way to do service communication.

  • Both backward and forward compatible is important.

• Documenting your services

  • Ensuring developers can use them in the first place.

  • At least, you should provide an API doc or README.

What have we learned today?

• The sidecar motocross is dangerous.

• The sidecar pattern is helpful to reduce system complexity by reusing common logic and abstracting trivial tasks.

• Service design matters in both performance and maintenance.

• In Umbo, we are really keen on adopting and practicing state-of-the-art software engineering ways to improve products and our career paths.