System Events

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System Events
NATS servers leverage Accounts support and generate events such as:
account connect/disconnect
authentication errors
server shutdown
server stat summary
In addition the server supports a limited number of requests that can be used to query for account connections, server stat summaries, and pinging servers in the cluster.
These events are enabled by configuring system_account and subscribing/requesting using a system account user.
​Accounts are used so that subscriptions from your applications, say >, do not receive system events and vice versa. Using accounts requires either:
​Configuring authentication locally and listing one of the accounts in system_account
Or by using decentralized authentication and authorization via jwt as shown in this Tutorial. In this case system_account contains the account public key.
Available Events and Services
The system account publishes messages under well known subject patterns.
Server initiated events:
$SYS.ACCOUNT.<id>.CONNECT (client connects)
$SYS.ACCOUNT.<id>.DISCONNECT (client disconnects)
$SYS.ACCOUNT.<id>.SERVER.CONNS (connections for an account changed)
$SYS.SERVER.<id>.CLIENT.AUTH.ERR (authentication error)
$SYS.ACCOUNT.<id>.LEAFNODE.CONNECT (leaf node connects)
$SYS.ACCOUNT.<id>.LEAFNODE.DISCONNECT (leaf node disconnects)
$SYS.SERVER.<id>.STATSZ (stats summary)
In addition other tools with system account privileges, can initiate requests (Examples can be found here):
$SYS.REQ.SERVER.<id>.STATSZ (request server stat summary)
$SYS.REQ.SERVER.PING (discover servers - will return multiple messages)
​Monitoring endpoints as listed in the table below are accessible as system services using the following subject pattern:
$SYS.REQ.SERVER.<id>.<endpoint-name> (request server monitoring endpoint corresponding to endpoint name.)
$SYS.REQ.SERVER.PING.<endpoint-name> (from all server, request server monitoring endpoint corresponding to endpoint name - will return multiple messages)
Endpoint
Endpoint Name
​General Server Information​
VARZ
​Connections​
CONNZ
​Routing​
ROUTEZ
​Gateways​
GATEWAYZ
​Leaf Nodes​
LEAFZ
​Subscription Routing​
SUBSZ
​JetStream​
JSZ
​Accounts​
ACCOUNTZ
"$SYS.REQ.ACCOUNT.<account-id>.<endpoint-name>(from all server, request account specific monitoring endpoint corresponding to account id and endpoint name - will return multiple messages)
Endpoint
Endpoint Name
​Connections​
CONNZ
​Leaf Nodes​
LEAFZ
​Subscription Routing​
SUBSZ
​JetStream​
JSZ
​Account​
INFO
Servers like nats-account-server publish system account messages when a claim is updated, the nats-server listens for them, and updates its account information accordingly:
$SYS.ACCOUNT.<id>.CLAIMS.UPDATE
With these few messages you can build useful monitoring tools:
health/load of your servers
client connects/disconnects
account connections
authentication errors
Local Configuration
To make use of System events, just using accounts, your configuration can look like this:
accounts: {
    USERS: {
        users: [
            {user: a, password: a}
        ]
    },
    SYS: { 
        users: [
            {user: admin, password: changeit}
           ]
    },
}
system_account: SYS
Please note that applications now have to authenticate such that a connection can be associated with an account. In this example username and password were chosen for simplicity of the demonstration. Subscribe to all system events like this nats sub -s nats://admin:[email protected]:4222 ">" and observe what happens when you do something like nats pub -s "nats://a:[email protected]:4222" foo bar. Examples on how to use system services can be found here.
Configuring Subject Mapping
System Events & Decentralized JWT Tutorial
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Outline
Available Events and Services
Local Configuration