What is linkerd?

What is linkerd?

Service mesh

Distributed applications

What is it actually?

• Layer 5 proxy
  • speaks HTTP, Thrift, HTTP/2, gRPC, etc (not raw TCP)
  • Deals with requests/responses
• Based on Finagle
• Runs as a sidecar process, nt a library

Ok but why?

• Service discovery
• Load balancing - reduce tail latency
• Retries - improve success rate
• Circuit breakers - improve resilience
• Metrics and Tracing - observability
• Other stuff - transport security, timeouts, deadlines, dynamic routing, per-request routing, ...

Ok but why?

• Network communication is complicated
• Apps shouldn't have to reinvent the wheel
• Libraries are language specific

Service mesh

Client side load balancing

• Power of two choices (P2C): Least Loaded
• Power of two choices (P2C): Peak EWMA
• Aperture: Least Loaded
• Heap: Least loaded

Client side load balancing

How it works

Dtabs (delegation tables)

• lists of routing rules
• take a list of logical paths and transform them to an actual path
• Bullet Three

Namers

• Take the path following them and convert it to an address
• After a namer is run routing is considered complete

Example

/iceCreamStore    => /smitten;
/smitten/try      => /smittenLocation/waitInLine/thenTry;
/smittenLocation  => /sanfrancisco/octavia/432;
/california       => /USA/CA;
/sanfrancisco     => /california/SF;

/iceCreamStore/try/allFlavors

An actual example

/svc => /#/io.l5d.consul/dc1;

/svc/ubo

Routing in depth