keyrouter

keyrouter

usage: keyrouter [<flags>]

A simple microservice for consistent hashing of service entries

Flags:
  --help                    Show context-sensitive help (also try --help-long and --help-man).
  --services=services.toml  location of services.toml
  --address=:8080           address to bind to
  --log-level="INFO"        minimum log level
  --version                 Show application version.

This is a simple service that maps keys to one or more service endpoint nodes in a consistent manner. Here consistent means that as the number of available nodes changes over time, the majority of keys should continue to map the same nodes. Thus, these nodes can be used for "sticky sessions" or sharding a key space. Multiple nodes can be returned to support shard replication or similar scenarios.

Services.toml file

Services should be defined in a services.toml file, of the form:

[[Services]]
  Name = "foo"
  Nodes = [
    "foo1:8080",
    "foo2:8080",
  ]

[[Services]]
  Name = "bar"
  Nodes = [
   "bar1:8080",
   "bar2:8080",
  ]

The values in Nodes are not validated in any way, but are typically service endpoints.

Reload on SIGHUP

The services.toml file is reloaded when receiving the SIGHUP signal, and added or removed entries for each service are updated.

Consul-Template Usage

This microservice is meant to be fed an up-to-date services.toml via a service discovery system; we suggest using consul-template. services.toml.tmpl is a very cut and dry consul-template template that would render all services registered with Consul. This can be used like:

consul-template -template services.toml.tmpl:/tmp/services.toml -exec keyrouter --services /tmp/services.toml -exec-reload-signal SIGHUP

This will run consul-template in daemon mode, which will in turn exec keyrouter and send it a SIGHUP whenever the services.toml file changes.

Requesting Consistent Service Entries

To get a set of consistent entries from a service, POST a request to /service/:servicename with the following arguments:

• key: The key to hash on.
• min: The minimum number of entries to return
• max: The maximum number of entries to return

Arguments can be sent as query strings, form data, or JSON. All three of these examples are equivalent:

• curl -v 'http://:8080/service/bar?key=ryans&min=1&max=3'
• curl -v http://:8080/service/bar -F "key=ryans" -F "min=1" -F "max=3"
• curl -v http://:8080/service/bar -H "Content-Type: application/json" --data '{"key":"ryans","min":1,"max":3}'

The response is a JSON-encoded array of between min and max members, which represent the N members "closest" to the input key in the service hash ring:

curl http://:8080/service/bar -H "Content-Type: application/json" --data '{"key":"k","min":1,"max":3}'
["bar1:8080","bar2:8080"]

Importantly different input key values will return the services in a different, but consistent order. If the available nodes for a service change over time, keys should largely stay mapped to the same nodes.