Synapse

Synapse is a Service discovery mechanism. It watch servers for services in a backend and report status in a router. This simplify service communication with backends and allow auto discovery & hot reconfiguration of the communication. This provide better services discovery and fault-tolerant communication between services

At BlaBlaCar, we use a synapse for each service node that want to communicate with another service and discover those backend nodes (> 2000). Nerve report node statuses to a Zookeeper and synapse watch it to update a local Hapoxy. All outgoing communication is going through this haproxy.

Airbnb

Go-Synapse is a go rewrite of Airbnb's Synapse with additional features.

Installation

Download the latest version on the release page.

Create a configuration file base on the doc or examples.

Run with ./synapse synapse-config.yml

Building

**** Just clone the repository and run ./gomake

Configuration

It's a YAML file. You can find examples here

Very minimal configuration file with only one service :

routers:
  - type: console
    eventsBufferDurationInMilli: 500
    services:
      - serverSort: random          # random, name, date
        watcher:
          type: zookeeper
          hosts: ['localhost:2181']
          path: /services/api/myapi
        serverOptions:              
          ...                       # depend on router type
        routerOptions:              
          ...                       # depend on router type

Root attributes:

logLevel: info
apiHost: 127.0.0.1
apiPort: 3454
routers:
    ...

Router config

Router console

Nothing special to configure for this router.

...
routers:
  - type: console
    services:
      - ...

Router haproxy

Router have haproxy specific attributes, but there is also services attributes

...
routers:
  - type: haproxy
    configPath: /tmp/hap.config
    reloadCommand: [./examples/haproxy_reload.sh]
    reloadTimeoutInMilli: 1000
    reloadMinIntervalInMilli: 500
    global:                                               # []string
      - stats   socket  /tmp/hap.socket level admin
    defaults:                                             # []string
    listen:                                               # map[string][]string
      stats:
         - mode http
         - bind 127.0.0.1:1936
         - stats enable

    services:
      - watcher:
          ...
        serverOptions: check inter 2s rise 3 fall 2
        routerOptions:
          frontend:
            - mode tcp
            - timeout client 31s
            - bind 127.0.0.1:5679
          backend:
            - mode tcp
            - timeout server 2m
            - timeout connect 45s

serverOptions support minimal templating:

serverOptions: cookie {{sha1String .Name}} check inter 2s rise 3 fall 2
serverOptions: cookie {{randString 10}} check inter 2s rise 3 fall 2
serverOptions: cookie {{.Name}} check inter 2s rise 3 fall 2

Router template

...
routers:
  - type: template
    destinationFile: /tmp/notexists/templated
    templateFile: ./examples/template.tmpl
    postTemplateCommand: [/bin/bash, -c, "echo 'ZZ' > /tmp/DDDD"]

    services:
      - watcher:
          ...

Services

routers:
  - type: ...

    services:
      - name: db-read
        watcher:
           ...
        serverCorrelation: # this will remove the first server declared in otherService from this service
          type: excludeServer
          otherServiceName: db-write
          scope: first

Watcher config

zookeeper watcher

routers:
  - type: ...

    services:
        - watcher:
            type: zookeeper
            hosts: [ 'localhost:2181', 'localhost:2182' ]
            path: /services/es/es_site_search
            timeoutInMilli: 2000