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Internal cache Pro

imgproxy Pro provides an internal cache that stores processed images on disk or in cloud storage. This cache can act as both a primary and a secondary cache, serving as a fallback when your CDN cache misses.

tip

While putting a CDN in front of imgproxy is and will always be a best practice, the internal cache provides long-term storage for cases that require an additional caching layer.

Why use internal cache?​

The internal cache provides long-term persistent storage for processed images, unlike CDNs, which typically delete rarely accessed content. It stores images in a single location rather than across multiple edge stores, eliminating cache misses when requests hit different edges. The cache is designed specifically for imgproxy, working seamlessly with features like modern image format detection and client hints support that generic external caches don't understand by default.

The cache is protected by the same security measures as imgproxy itself, including URL signatures and processing restrictions. Importantly, URL signatures are not part of the cache key, so you can rotate keys or use multiple key/salt pairs without invalidating cached images. You maintain full control over where the cache is stored and how it integrates with your infrastructure.

Configuration​

You need to define the following config variables to enable the internal cache:

  • IMGPROXY_CACHE_USE: the cache storage adapter to use. Can be fs, s3, gcs, abs (Azure Blob Storage), or swift (OpenStack Swift). When blank, the cache is disabled. Default: blank
  • IMGPROXY_CACHE_PATH_PREFIX: (optional) a path prefix for the cache files. This can be useful to organize cache files in a specific directory structure. Default: blank
  • IMGPROXY_CACHE_BUCKET: (optional) the bucket name for cloud storage adapters (S3, GCS, ABS, Swift). When using the filesystem adapter, this can be used as an additional path component. Default: blank
  • IMGPROXY_CACHE_KEY_HEADERS: (optional) a list of HTTP request headers (comma-separated) to include in the cache key. This allows caching different versions of the same image based on request headers. Default: blank
  • IMGPROXY_CACHE_KEY_COOKIES: (optional) a list of HTTP request cookies (comma-separated) to include in the cache key. This allows caching different versions of the same image based on cookies. Default: blank
  • IMGPROXY_CACHE_REPORT_ERRORS: When true, imgproxy will report cache errors instead of silently falling back to processing without cache. Default: false
  • IMGPROXY_CACHE_SHUTDOWN_TIMEOUT: (optional) the maximum time imgproxy will wait for pending background cache writes to complete during a graceful shutdown. Default: 5s
  • IMGPROXY_CACHE_PROCESSING_ENABLED: (optional) when true, imgproxy will cache processed images. Default: true
  • IMGPROXY_CACHE_INFO_ENABLED: (optional) when true, imgproxy will cache /info endpoint responses. Default: true
  • IMGPROXY_CACHE_SOURCE_ENABLED_FOR: (optional) a comma-separated list of source URL schemes for which imgproxy will cache downloaded source images. Supported values are fs, s3, gcs, abs, swift, http, https, and all. all enables source caching for all schemes in the source URL. When blank, source caching is disabled. Default: blank

Source image caching​

If you process remote images, like ones from third-party HTTP sources, you may want to cache source images in your storage to keep them close to imgproxy. You can enable source image caching by setting IMGPROXY_CACHE_SOURCE_ENABLED_FOR to the list of source URL schemes to cache, for example http,https. This way, imgproxy caches the source image on the first transformation and fetches it from the cache for subsequent ones.

Supported values are fs, s3, gcs, abs, swift, http, https, and all (enables source caching for all schemes in the source URL). Note that the value selects which source schemes are cached, not which storage is used for the cache.

Storage configuration​

The internal cache supports all the storage backends that imgproxy can read source images from: local filesystem, Amazon S3 and compatible services (Cloudflare R2, DigitalOcean Spaces, MinIO, etc.), Google Cloud Storage, Microsoft Azure Blob Storage, and OpenStack Swift.

Configure the storage backend using IMGPROXY_CACHE_* variables:

Cache key​

The cache key for processed images and /info responses is generated based on:

  • Source image URL
  • Processing options
  • Output format
  • Optional: Request headers specified in IMGPROXY_CACHE_KEY_HEADERS
  • Optional: Request cookies specified in IMGPROXY_CACHE_KEY_COOKIES

URL signature is not part of the cache key, allowing key rotation without invalidating the cache.

Source cache key​

When source image caching is enabled, cached sources use their own separate key, based on:

  • Source image URL
  • Optional: Request headers specified in IMGPROXY_CACHE_KEY_HEADERS
  • Optional: Request cookies specified in IMGPROXY_CACHE_KEY_COOKIES

Unlike the processed-image cache key, it doesn’t include processing options or the output format because it stores the downloaded source image, not a processed variant. It also doesn’t include the cachebuster value, so busting the processed-image cache doesn't invalidate the cached source.

Cache tags​

imgproxy Pro can attach cache tags to a cache entry using the cache_tags processing option:

cache_tags:%tag1:%tag2:...:%tagN
ct:%tag1:%tag2:...:%tagN

Each tag can be up to 256 characters long and must consist of visible ASCII characters (character codes 33-126), excluding commas. We consider at most 50 tags per request; any beyond that are silently dropped.

The tags are also written to the response headers, so a CDN in front of imgproxy can use them for tag-based cache invalidation. Use the IMGPROXY_CACHE_TAGS_FORMAT config to choose which format(s) the tags are written in.

Bypassing the cache​

imgproxy Pro can bypass the internal cache for a single request using the bypass_cache processing option:

bypass_cache:%bypass:%bypass_source
bc:%bypass:%bypass_source

Requires IMGPROXY_ALLOW_BYPASS_CACHE set to true. bypass_source is optional, and equals to bypass if not specified, hence, when only bypass is set, both processing and source cache are ignored.

Default: 0:0

Limitations​

  • No manual cache invalidation: Currently, imgproxy doesn't provide a built-in means to invalidate the cache. However, imgproxy includes the cachebuster in the cache key, so you can use it to force cache invalidation when needed. Most storage offerings also support object expiration, so you can set a reasonable expiration time for cached images.

How it works​

When a request comes in:

  1. imgproxy checks the URL signature (if enabled).
  2. imgproxy generates the cache key from the request parameters.
  3. imgproxy checks if a cached processed image exists in the configured storage.
  4. If the cached image exists and is valid, imgproxy serves it directly.
  5. If not, and source image caching is enabled, imgproxy checks the source cache (using its own separate key) before downloading the source image:
    • On a hit, imgproxy uses the cached source bytes instead of re-downloading them.
    • On a miss, imgproxy downloads the source image and caches it in the background.
  6. imgproxy processes the image, serves the result, and stores it in the cache in the background — the response isn't delayed while it waits for the cache write to finish.

Cache writes (both processed-image and source) always happen in the background this way. On a graceful shutdown, imgproxy waits up to IMGPROXY_CACHE_SHUTDOWN_TIMEOUT for any still-pending writes to finish before exiting.