Implementing ISR in Jamstack: A Decision Guide Comparing ISR, SSR & SSG

Problem and takeaway

You manage a Jamstack site built with Next.js and need to publish updated content without triggering a full site rebuild, while still benefiting from CDN caching and avoiding the overhead of real-time server-side rendering for every request.

Useful takeaway: Incremental Static Regeneration (ISR) lets you keep static-generated pages that are automatically refreshed after a set interval, giving you the best of both worlds.

Decision state and constraints

Before choosing a regeneration strategy, consider the following constraints:

• Content update frequency: how often does the data change?
• CDN caching requirements: do you need edge caching for performance?
• Server load tolerance: can your origin handle per-request rendering?
• Deploy pipeline constraints: does your team prefer zero-deploy updates?

Trade-offs

• ISR introduces a brief stale-while-revalidate period; content may be up to the revalidate interval old before regeneration occurs.
• Full SSR increases server load and reduces CDN caching benefits, but provides truly real-time data on every request.
• Pure SSG offers the fastest CDN delivery but requires a new build and redeploy for any content change.

Concrete ISR implementation

In Next.js (Pages Router), add the revalidate option to getStaticProps:

export async function getStaticProps(context) { return { props: {}, revalidate: 60, } // regenerate every 60 seconds}

Verification

After deploying, run the following command to check the caching header:

curl -I https://your-site.com/page

Expected response header: Cache-Control: public, s-maxage=60 (the value matches your revalidate seconds).

You can also inspect the generated page under .next/static/pages or use Next.js dev tools to confirm the page exists with the expected revalidate timestamp.

Limitations

• ISR does not support true real-time data; the revalidate interval sets the maximum staleness of served content.
• Revalidate only applies to pages generated via getStaticProps; dynamic routes or API routes require different handling.
• Very short revalidate values (e.g., < 5 seconds) increase regeneration frequency and may impact build performance.