@sealsystems/consul

@sealsystems/consul provides service discovery based on Consul.

Installation

npm install @sealsystems/consul

Quick start

First you need to add a reference to @sealsystems/consul within your application.

const consul = require('@sealsystems/consul');

Then call connect to register your service with Consul.

await consul.connect({
  id: 'my-service-id',
  name: 'my-service-name',
  serviceUrl: 'http://localhost:3000', // URL of my service
  consulUrl: 'http://localhost:8500', // URL of a Consul server
  dnsPort: '8600' // Optional non-default port of the DNS server
});

// Your service is now registered

You may omit the hostname of your service in serviceUrl (e.g. by setting it to http://:3000). In this case, your service is assumed to run on the same host as the Consul agent.

For the service, a new health check with a TTL of 10 seconds will be created. A heartbeat request will be sent every 5 seconds to Consul in order to prevent the TTL to expire.

By default, the status of a service is warn. Consul also recognizes the states passand fail. Call the appropriate function, to change the state of your service. To set it to e.g. pass, use:

await consul.pass();

To get all nodes providing a specific service, call getNodes. It uses the same interface as node-consul's consul.catalog.service.nodes function.

Watching a service

Use the watch function to receive notifications when the group of nodes that provide a service has been changed:

const watch = consul.watch({
  serviceName: 'my-service-name', // Name of the service to watch
  consulUrl: 'http://localhost:8500' // URL of a Consul server
});

watch.on('change', (nodes) => {
  // The 'nodes' array contains data about all nodes that provide the watched service
});

watch.on('error', (err) => {
  // ...
})

The change event is raised whenever a new node provides the service or a node is no longer available. Only nodes with passing health checks are regarded as available. At the start of the watch, the event is also immediately raised with an array of all currently active nodes.

A node object contains the following properties:

• host: The address of the node
• node: Consul's node name
• port: The port used by the service

Custom Consul domain

By default the domain consul will be used to resolve a service. E.g. the service checkout will be expanded to checkout.service.consul. If another domain is given in Consul's configuration, you must set the environment variable CONSUL_DOMAIN accordingly.

If you configure Consul to use e.g. sealsystems.com as the domain, you must also define this domain via the environment variable:

CONSUL_DOMAIN=sealsystems.com

This will change the expanded service name given above to: checkout.service.sealsystems.com

Using in cloud environment

To enable cloud environment set the environment variable SERVICE_DISCOVERY to the value cloud. To disable cloud environment unset the variable or set it to the value consul. Additionally the environment variable SERVICE_DISCOVERY_PORT defines the https port all services are available. Default is 3000.

Initializing without connecting first

It is assumed that you call consul.connect first. This will establish the connection to the local Consul agent. The other functions (e.g. consul.getHostname) will throw an error if this connection has not been initialized.

If you do not want to register a service check via consul.connect, just call consul.initialize instead. This will only connect to the Consul agent. Now, you can use most of the other functions.

Please note: consul.heartbeat, consul.lookup, consul.resolveService require consul.connect to be called. They will not work properly if you only call consul.initialize.

Get configuration from consul kv store

To read configuration from consul kv store, you can use the consul.setEnv function. It will read all key-value pairs from the service path (starting with dc/home/env/service/...) and set them as environment variables. The path must be given without the leading slash.

await consul.setEnv(options);

The method initializes the connection to the local Consul agent. The following options are available:

• consulUrl: The URL of a consul server.
• consulConfig: The path and filename to a JSON file, containing a consul.address property of format host:port like the envconsul.json file. Defaults to /opt/seal/etc/envconsul.json on linux and $ProgrammData\SEAL Systems\config\envconsul.json on windows.
• defaultUrl: The URL of a Consul server, if no other URL is given or the consulConfig file could not be read.
• serviceName: The name of the service to read the configuration for. If not given, the name of the service is read from the environment variable SERVICE_NAME.
• serviceTags: An array of service tags. If not given, the tags of the service are read from the environment variable SERVICE_TAGS. Tags are optional.
• retries: The number of retries to get the configuration from consul. Defaults to 10.

If no URL to a consul server could be determined an exception is thrown. It is recommended to set at least the defaultUrl option.

Running the build

To build this module use roboter.

bot