Mitigating bot and caching issues with publicly accessible images

[hud-code (Zach Hudson)]

Understanding the Problem

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Context

Publicly accessible images often attract unwanted attention from bots and external caching mechanisms, causing confusion and frustration for users managing these assets. This issue commonly occurs when content is shared on social media platforms which maintain their own independent caches, often disregarding server-side updates.

Understanding external caching mechanisms and utilizing Vercel’s tools for managing image assets and bot access is crucial to ensure the right content reaches the intended audience. By addressing these issues, users can improve site performance, refine SEO strategies, and reduce unwanted bot traffic.

Example scenario

Consider an e-commerce business that frequently updates its product images and descriptions. They need real-time content updates and precise control over how their products are indexed and displayed across various platforms. Managing public images while preventing unintended caching by third-party bots (such as social media crawlers) is a common challenge they face.

This scenario underscores the importance of implementing effective strategies to mitigate bot and caching issues with publicly accessible images.

Common pitfalls

Users are confused over different types of caching, misunderstanding the limitations of robots.txt, overlooking the importance of remotePatterns configuration in Vercel, and relying too heavily on solutions like firewall rules.

Users also struggle to differentiate between server-side caching they can control and client-side caching managed by external services, while also assuming all bots will respect robots.txt directives when some may ignore these rules.

Additionally, many overlook the powerful remotePatterns settings in Vercel that can block unwanted optimizations or caching of specific image paths, instead opting for short-term fixes that don’t address the root issue of image accessibility to unwanted agents.

Recommended Approach

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Key Considerations

1. Cache Ownership: Differentiate between Vercel’s server-side cache and external client-side caches, like those maintained by social media platforms.
2. Controlled Access with remotePatterns: Use remotePatterns to specify which external images are allowed for optimization, creating an allowlist that ensures only trusted source images can be optimized.
3. Crawling and Indexing: Understand that some bots respect robots.txt directives while others may not, and plan accordingly.
4. Strategic Use of Vercel Firewall Rules: Reserve firewall rules for bot control and use remotePatterns as a more stable solution.

Steps to Follow

1. Evaluate Current Cache and Access Needs: Assess which images are being accessed by bots and whether certain paths or images should be excluded from optimization.
2. Define remotePatterns Rules: Configure remotePatterns in Vercel to specify which external image sources, folders, or filenames are allowed to be optimized and cached, creating an allowlist for trusted image resources.
3. Implement robots.txt Rules: Add rules to robots.txt for compliant bots, such as Disallow: /_next/image*, to prevent unnecessary indexing.
4. Set Vercel Firewall Rules: For persistent bot issues, block specific user agents with firewall rules. Use this approach to limit unwanted access while updating the remotePatterns.
5. Educate Team and Users: Share knowledge about how external bots and caching work, so team members and clients understand the limitations of server-side control over these elements.

Resources

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• Next.js Documentation on overrideSrc: Information on using overrideSrc in Next.js, though not recommended as a sole solution.
• Vercel Documentation on remotePatterns: Overview of remotePatterns configuration to block specific image paths from optimization.
• Vercel Documentation on Firewall Rules: Guide to setting firewall rules for blocking specific user agents.