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NATS Configuration Contexts

Metadata Value
Date 2021-12-14
Author @ripienaar
Status Partially Implemented
Tags client

Background

A nats context is a named configuration stored in a configuration file allowing a set of related configuration items to be stored and accessed later.

In the nats CLI this is used extensively, for example nats stream ls --context orders would load the orders context and configure items such as login credentials, servers, domains, API prefixes and more.

The intention of the ADR is to document the storage of these contexts so that clients can, optionally, support using them.

Version History

Date Revision
2020-08-12 Initial basic design
2020-05-07 JetStream Domains
2021-12-13 Custom Inbox Prefix

This reflects a current implementation in use widely via the CLI as such it's a stable release. Only non breaking additions will be considered.

Design

Today the design is entirely file based for maximum portability, later we can consider other options like S3 buckets, KV stores etc.

Configuration Paths

There is generally no standard for what goes on in a users home directory on a Unix system. Recently the Free Desktop team have been working on XDG Base Directory Specification that specifies in detail where configuration, data, binaries and more are to be stored in a way that's compatible with Linux desktops like KDE and Gnome but also with systems such as systemd.

We therefore based the design on this specification as a widely supported standard.

File Description
~/.config The default location for user configuration, configurable using XDG_CONFIG_HOME
~/.config/nats Where all NATS related user configuration should go
~/.config/nats/context.txt The current selected (default) context, would contain just ngs
~/.config/nats/context/ngs.json The configuration for the ngs context

While this is Linux centered it does work on Windows, we might want to consider a more typical path to replace ~/.config there and keep the rest as above.

Context content

The ~/.config/nats/context/ngs.json file has the following JSON fields:

Key Default Description
description A human friendly description for the specific context
url nats://localhost:4222 Comma seperated list of server urls
token Authentication token
user The username to connect with, requires a password
password Password to connect with
creds Path to a NATS Credentials file
nkey Path to a NATS Nkey file
cert Path to the x509 public certificate
key Path to the x509 private key
ca Path to the x509 Certificate Authority
nsc A nsc resolve url for loading credentials and server urls
jetstream_domain The JetStream Domain to use
jetstream_api_prefix The JetStream API Prefix to use
jetstream_event_prefix The JetStream Event Prefix
inbox_prefix A prefix to use when generating inboxes

All fields are optional, none are marked as omitempty, users wishing to edit these with an editor should known all valid key names.

Above settings map quite obviously to client features with the exception of nsc, the nsc key takes a URL like value, examples are:

  • nsc://operator
  • nsc://operator/account
  • nsc://operator/account/user
  • nsc://operator/account/user?operatorSeed&accountSeed&userSeed
  • nsc://operator/account/user?operatorKey&accountKey&userKey
  • nsc://operator?key&seed
  • nsc://operator/account?key&seed
  • nsc://operator/account/user?key&seed
  • nsc://operator/account/user?store=/a/.nsc/nats&keystore=/foo/.nkeys

The context invokes nsc generate profile <url>, the responce will be non zero exit code for error else a structure like:

{
  "user_creds": "<filepath>",
  "operator" : {
     "service": "hostport"
   }
}

This will configure the creds and url parts of the context. If either url or creds is specifically configured in the Context those will override the answer from nsc.

See nsc generate profile --help for details.

Sample Usage APIs

I don't think we really want to dictate standard APIs here, in Go we have 2 main ways to use the package.

It's also fine to delegate management of these to the nats CLI.

A very basic and quick way to just connect to a specific context:

nc, _ := Connect(os.GetEnv("CONTEXT"), nats.MaxReconnects(-1))

Here Connect will construct []nats.Option based on the context settings and append the user supplied ones to the list.

A way to load a context and optionally override some options:

nctx, _ := Load(os.GetEnv("CONTEXT"), WithServerURL("nats://other:4222"))
nc, _ := nctx.Connect(nats.MaxReconnects(-1))

When name is empty it will use the current selected context, if no context is selected and name is empty it's an error.