Single-Instance Deployment

You might say

Run this service as one instance and explain the short outage during restart, while separating in-memory task risk from durable data.

Single-instance deployment keeps exactly one running replica of a service in its environment.A background service with a replica count of 1 sends requests to one running instance. A release or crash restart can make it briefly unavailable, and in-memory work that was not written to durable storage may be lost. Single-instance deployment is not the Singleton pattern and does not mean data cannot be durable: it describes the number of runtime replicas, while a database or other durable store can exist separately.

Know first

Deployment Database

Single-Instance Deployment

Where request and restart risk concentrates with one instance

Single-instance web servicereplicas = 1

traffic / network

trafficall to web-1

web-1Healthy

standbynone

EvidenceThe platform shows one running replica

All live traffic depends on one instance.

What to see clearly in single-instance deployment

The only replica defines the availability window: When one running instance handles the service, a release, crash, or maintenance event leaves no other replica of the same service to take over requests. Brief unavailability during restart is an expected risk; a successful deployment job does not mean users remain continuously connected.

Move required state out of process memory: Unfinished work in process memory may disappear when the instance stops, while records in durable storage can be read again after recovery. Verify service recovery, durable data, and which in-memory tasks may be lost separately. This improves recovery evidence but does not give one instance automatic failover.

An internal room-booking service can run as one instance: A low-traffic internal room-booking service can run as one instance for a simpler deployment. However, every booking entry point becomes briefly unavailable during a release, so choose an acceptable maintenance window and state this risk clearly.

Quick checkChoose the best answer

A single-instance service is restarting and users temporarily cannot open the page. Which judgment and verification are accurate?

Accept a brief restart outage and confirm durable data is readable after recoveryDelete the Singleton object in code to make deployment multi-instance and avoid the interruptionOnce the service is online again, assume every task kept in memory before restart still exists

You can say this to an AI Agent

Deploy this background service as a single instance and state the restart unavailability window when the replica count is 1. Check that task state is written to durable storage instead of keeping recoverable work only in process memory. Restart it once, confirm the service recovers and existing data is readable, and report the availability risk of the single instance.

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