Each test is 5 questions with varying difficulty.
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Webhooks vs Polling is a foundational topic in modern API design, focusing on the trade-offs between push-based event notification and pull-based state synchronization. In 2026, as distributed systems scale to handle millions of real-time events, choosing the correct integration pattern is critical for minimizing latency and infrastructure costs. This topic is essential for Backend, API, and System Design engineers. Interviewers use this to gauge a candidate's understanding of network efficiency, state consistency, and fault tolerance. Junior engineers are expected to explain the basic mechanics and when to choose one over the other based on latency requirements. Senior engineers must demonstrate deep knowledge of failure modes, such as webhook delivery retries, idempotency requirements, and the impact of polling frequency on database load.
The choice between webhooks and polling directly impacts system performance and operational costs. Polling, while simpler to implement, often leads to 'polling overhead' where servers waste CPU and network bandwidth checking for updates that haven't occurred. In high-scale systems, this can result in unnecessary database load and increased latency. Conversely, webhooks provide near-instant updates but introduce complexity regarding security, delivery guarantees, and server availability. Understanding this trade-off is high-signal because it reveals whether a candidate prioritizes system efficiency and robustness over simple implementation. In 2026, with the rise of AI-driven real-time agents and streaming data, the ability to design resilient event-driven pipelines—specifically handling webhook retries and ensuring idempotency—is a key differentiator for senior roles. A strong candidate will discuss how to mitigate webhook delivery failures using outbox patterns and how to optimize polling using conditional GET requests (ETags).
The architectural flow for webhooks involves an event trigger, a delivery service, and a receiver endpoint. Polling involves a client-side loop, a request handler, and a database query layer.
[Event Source]
↓
[Webhook Dispatcher] [Polling Client]
↓ ↓
[HTTP POST Request] [HTTP GET Request]
↓ ↓
[Receiver Endpoint] [API Server]
↓ ↓
[Process Logic] [Database Query]
↓ ↓
[Ack/Response] [Return Data]Store events in a local database table and use a separate background worker to retry delivery until successful.
Trade-offs: Ensures delivery but requires careful handling of duplicate events.
Increase the polling interval dynamically if the server returns no new data.
Trade-offs: Reduces load but increases latency during periods of inactivity.
Validate the 'X-Hub-Signature' header using a shared secret to ensure the payload originated from the expected source.
Trade-offs: Adds CPU overhead but prevents spoofing attacks.
| Reliability | Webhooks require retries, dead-letter queues, and idempotency keys to handle network partitions. |
| Scalability | Polling scales poorly with client count; webhooks scale better but require high-throughput dispatchers. |
| Performance | Webhooks offer sub-second latency; polling latency is bound by the polling interval. |
| Cost | Polling increases infrastructure costs due to redundant requests; webhooks reduce request volume. |
| Security | Webhooks require HMAC signing and TLS; polling relies on standard API authentication. |
| Monitoring | Track delivery success rates, retry counts, and latency for webhooks; track request frequency and 304 hit rates for polling. |
Choose webhooks when you need real-time updates and can afford the complexity of managing a public-facing endpoint. They are ideal for high-frequency events where latency is critical. Choose polling if the client is behind a firewall, the update frequency is very low, or you need a simpler, pull-based integration.
Implement a retry policy with exponential backoff. Use a dead-letter queue (DLQ) to store events that fail after the maximum number of retries for manual inspection. Always ensure your receiver is idempotent so that retried events do not cause duplicate state changes.
Webhooks are stateless, asynchronous, and event-driven; they use standard HTTP POST requests. WebSockets are stateful, full-duplex, and persistent; they maintain a long-lived connection between client and server. Webhooks are better for discrete events, while WebSockets are better for continuous streams.
Always use HTTPS to encrypt data in transit. Validate the sender using HMAC signatures (e.g., X-Hub-Signature) to ensure the request is authentic. Optionally, use IP whitelisting if the sender provides a static range of IP addresses.
Not necessarily. Polling is inefficient if done too frequently, but it can be optimized using conditional GET requests (ETags). If the data changes rarely, a long polling interval or conditional checks can be very efficient and simpler to maintain than a full webhook infrastructure.
It occurs when many clients poll a server at the exact same interval, causing a massive spike in traffic. This can overwhelm the server and database. It is mitigated by adding 'jitter' (randomizing the interval) to spread out the requests.
Because webhooks are delivered over unreliable networks, senders often retry deliveries if they don't receive a timely acknowledgement. Without idempotency, your system might process the same event multiple times, leading to inconsistent state, such as double-charging a customer.
No, webhooks require the sender to reach your server directly. If you are behind a firewall, you must use polling or a persistent connection like WebSockets, or use a reverse proxy/tunneling service (like Ngrok) to expose your endpoint.
The dispatcher is the component that manages the delivery of events to registered clients. It handles retries, maintains delivery logs, and ensures that events are sent to the correct endpoints. It is often backed by a message queue to handle high volumes.
Ordering is difficult because retries can arrive out of sequence. To handle this, include a version number or a timestamp in the webhook payload. Your receiver should check these values and ignore older events if a newer one has already been processed.
AI Prep covers AI Agents, Generative AI, ML Fundamentals, NLP & LLMs and a lot more, with adaptive tests and daily challenges. Fully offline on Android. Free to try, one-time unlock for lifetime access.