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Graph/per-request-client-instantiation

Pattern

Singleton Client Reuse

per-request-client-instantiation

Creating HTTP/AWS client sessions per request breaks connection reuse because clients are instantiated outside a long-lived lifecycle, causing socket churn and losing state like cookies; the fix is lazy singleton initialization tied to app startup.

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Updated5/30/2026

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30 linked nodes

Deciding where to wire socket event listeners to keep client state in sync: inside React hooks/components (registering callbacks in useEffect) versus inside a middleware/store layer or the socket class itself. The question also asks about the downsides of each approach.

new instances of QueryClient are being created every time the file is loaded — I have the following setup in my root file to create a singleton QueryClient instance. Tension: even though I expected to share the same instance across both server and client. Outcome: you can't send the QueryClient from the server to the client and you don't really want to do that.

the cache doesn't work across processes — workers might be pre-forked. Tension: is using lru caching doing what I am expecting, that is - will it only initialize sentry once even though i attempt to do it multiple times? Outcome: provided it's called within the same process.

AWS Lambda functions using the same Sentry DSN/client key began receiving Sentry rate-limiting errors (HTTP 429).

self._session = aiohttp.ClientSession() — from .singletons import SINGLETONS. Outcome: You can benefit from the lazy initialization inside the `startup` event.

trying to perform data processing during the application's startup. Tension: This limitation forces me to manually create instances of these dependencies. Outcome: this approach doesn't work as expected.

TestClient(app) will not start `async def lifespan(app: FastAPI):`. Tension: the written test fails. Outcome: This is all working fine, every 10 seconds `app.state.global_rw` is increased by one.

Every `boto3.Session()` call is costing me 50ms-100ms in latency — creating a new session at the beginning of every endpoint. Tension: it'd be great if I could just create a global one and have it never expire. Outcome: creating a global `boto3.Session`.

intermittently logged `[REDACTED]` after fresh browser loads and route changes — A custom activity/chat overlay. Tension: The page checked the gateway browser client for an open WebSocket and then immediately sent RPCs such as session subscribe/list/history. Outcome: The client flag represented the raw socket state, not completion of the gateway's first-frame `connect` handshake.

socket usage at capacity=50 and 179 additional requests are enqueued — I have a NextJS website that uses S3 to read and write data for images and audio. Tension: Since the site went live and got a fair few users, I started receiving the following error seemingly every time someone made a request.

The exception happens at build() — S3Client.builder() .region(Region.US_WEST_1) .credentialsProvider(StaticCredentialsProvider.create(awsCredentials)). Tension: java.lang.NoClassDefFoundError: software/amazon/awssdk/http/auth/scheme/NoAuthAuthScheme. Outcome: Adding http-auth-2.30.4.jar to the classpath resolves this issue and the Exception no longer occurs.

The HTTP request cannot be executed: The peer resets the connection. — When I try to upload files to S3 from storage via an application deployed on the stand. Tension: Everything is working locally. All files is uploading without errors. Outcome: com.amazonaws.SdkClientException exception.

HTTPClientError: An HTTP Client raised an unhandled exception: sequence item 0: expected str instance, bytes found — save it into a S3 bucket. Tension: My issue is I have added a python `requests` layer which somehow messed with how Lambda send the object to s3 using https. Outcome: The error is gone if I remove the layer.

Executing an authenticated AWS AppSync GraphQL mutation from a Next.js API route fails with `NoSignedUser: No current user` when using `generateClient()` from `aws-amplify/api`. Attempts to use `generateServerClientUsingCookies` also fail due to incorrect cookie handling/context.

I need to make sure it's only initialized once — my configuration object that's used everywhere inside the app. Tension: its contents as well as how it is initialized depend on a bunch of things that change depending on the deployment environment.

A Paho MQTT client is created on one React page, but a Disconnect button on another page needs to call client.disconnect(). Attempts to store the client object in a Redux store result in an empty object being saved.

Repeated authentication logic (updating Redux state, authorizing, and saving tokens) is duplicated across multiple createAsyncThunk services.

the first attempt to creata a connection is always falis with a timeout — initialize my pool with 5 connections in my .net6 application using postgres and Npgsql. Tension: first connection attempt or a connection after a longer period would immediately time out.

Devise does not provide a maximum session length for active sessions

HTTP request keeps accepting data after the size limit is exceeded, wasting server resources

The session identifier (req.sessionID) changed on every subsequent HTTP request from the React client to the Express server, preventing consistent session persistence.

the http method in the controller was returning the reactive method's output directly — This made the http response sync awaiting the reactor response and cancelling it upon http timeout. Outcome: The issue was resolved by invoking the reactor and subscribing to it from the controller and returning a dummy http success response.

Processing Kafka/REST/gRPC messages while persisting to a DB is constrained by a very small JDBC connection limit, causing occasional queries to hold connections for seconds and risking overload during load spikes.

Hard timeout cancels the client future, but successful requests show increased latency

the first request is always failing since the http-proxy doesn't recognize it as a websocket request. Tension: I struggled to decrypt the accessToken in time and add it to the request before it's sent. Outcome: for now it's not bothering me that much.

Got HTTP 400 with "missing mcp-session-id" on every call. Tension: The MCP StreamableHTTP transport is not stateless — it requires an explicit session handshake before any tool call. Outcome: Implement the full session lifecycle in the client.

heap use-after-free in two TLS 1.3 client extension serializers — lib/ext/key_share.c:key_share_send_params and lib/ext/pre_shared_key.c:client_send_params. Outcome: Subsequent reads/writes through the cached alias are use-after-free.

WebSocket connections to external services use Sandbox.WebSocket, not System.Net.WebSockets (sandboxed out) — In s&box. Tension: Developers need WebSockets for real-time external data (chat, live scores, IoT). The same URL restrictions as Http apply — no IP addresses, HTTPS/WSS only.

Dev hot-reload silently stops working — Next.js (App Router) and a WebSocket server in the same Node process. Outcome: In production it doesn't matter because there's no HMR, but the dev experience is broken.

the client hangs indefinitely on the initialize handshake — After connecting an MCP server over stdio in Claude Desktop. Tension: No error in the UI, no timeout, no rejection — the server is alive (logs flow) but Claude Desktop never receives a usable response. Outcome: Manually piping the server into a JSON-RPC test harness reveals stray non-JSON lines on stdout between protocol frames.

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