Handle errors and reconnect in Node.js

The code

const { OPCUAClient } = require("node-opcua");

(async () => {
  const client = OPCUAClient.create({
    endpointMustExist: false,
    connectionStrategy: {
      maxRetry: -1,          // retry forever
      initialDelay: 1000,
      maxDelay: 30000,       // cap the backoff
      randomisationFactor: 0.5,   // jitter: vital across a fleet
    },
    keepSessionAlive: true,
    requestedSessionTimeout: 60000,
  });

  client.on("backoff", (retry, delay) =>
    console.log(`retry ${retry}, next attempt in ${delay}ms`));
  client.on("connection_lost", () => console.log("connection lost"));
  client.on("connection_reestablished", () => console.log("reconnected"));
  client.on("start_reconnection", () => console.log("reconnecting..."));

  await client.connect("opc.tcp://opcua.umati.app:4840");
  const session = await client.createSession();

  session.on("session_closed", () => console.log("session closed"));
  session.on("keepalive_failure", () => console.log("keepalive failed"));

  console.log("running; the client now handles reconnection itself");
})();

What it prints

running; the client now handles reconnection itself
connection lost
reconnecting...
retry 1, next attempt in 1240ms
retry 2, next attempt in 2130ms
reconnected

Notes

• Set randomisationFactor. Without jitter, a fleet of collectors reconnects in lockstep after a network event and finishes the job the network event started.
• keepSessionAlive lets the client notice a dead session promptly instead of at the next read.
• Do not retry configuration errors. BadCertificateUntrusted and BadUserAccessDenied will fail identically forever: log once, alert, and stop.
• After reconnection, verify your monitored items are still reporting. A transferred subscription is the good case; a silently dead one is not.
• Classify before retrying: certificate and identity errors need a human, BadTooMany* means capacity, BadConnectionClosed is transient.

What breaks first

Last verified 7 September 2026 against OPC UA 1.05.07. OPC UA Connect is an educational resource and is not affiliated with the OPC Foundation.