Question 1

What is Incremental Static Regeneration (ISR)?

Accepted Answer

Serve static pages and regenerate them in the background after a revalidation period or on demand. Combines static speed with eventual freshness. Stale-while-revalidate semantics are common. Ideal for content that updates occasionally.

Question 2

How do you set a revalidate interval in App Router?

Accepted Answer

Export revalidate segment config or use fetch next: { revalidate: seconds }. Time-based revalidation refreshes after TTL. Prefer tagging + on-demand revalidation for editorial workflows when possible.

Question 3

What is on-demand revalidation?

Accepted Answer

Explicitly invalidate cached pages/data after a CMS publish via revalidatePath/revalidateTag. Gives editors immediate updates without short TTLs everywhere. Secure the revalidation API route with a secret.

Question 4

Explain revalidateTag vs revalidatePath.

Accepted Answer

Tag invalidates cached data fetches sharing a tag; path invalidates a route's cache entries. Tagging models domain entities (product:123). Paths are coarser. Design tag taxonomy early for scalable invalidation.

Question 5

What race conditions exist with ISR?

Accepted Answer

Concurrent regenerations, stampede after expiry, and users briefly seeing stale content. Understand stale-while-revalidate. For strong consistency needs, use dynamic rendering or carefully designed cache keys.

Question 6

When would you avoid ISR?

Accepted Answer

When correctness requires read-after-write consistency or per-request personalization. Checkout inventory, permissions, and financial data often need request-time reads. ISR is for cacheable public content.

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