Allow caching only in gateway mode. (#8232)

This PR changes cache on PUT behavior to background fill the cache
after PutObject completes. This will avoid concurrency issues as in #8219.

Added cleanup of partially filled cache to prevent cache corruption
- Fixes #8208

docs/disk-caching/DESIGN.md

@@ -5,7 +5,7 @@ This document explains some basic assumptions and design approach, limits of the
 ## Command-line
 
 ```
-minio server -h
+minio gateway <name> -h
 ...
 ...
   CACHE:
@@ -16,17 +16,18 @@ minio server -h
 ...
 ...
 
-  7. Start minio server with edge caching enabled on '/mnt/drive1', '/mnt/drive2' and '/mnt/export1 ... /mnt/export24',
+  7. Start MinIO gateway to s3 with edge caching enabled on '/mnt/drive1', '/mnt/drive2' and '/mnt/export1 ... /mnt/export24',
      exclude all objects under 'mybucket', exclude all objects with '.pdf' as extension
      with expiry up to 40 days.
      $ export MINIO_CACHE_DRIVES="/mnt/drive1;/mnt/drive2;/mnt/export{1..24}"
      $ export MINIO_CACHE_EXCLUDE="mybucket/*;*.pdf"
      $ export MINIO_CACHE_EXPIRY=40
      $ export MINIO_CACHE_MAXUSE=80
-     $ minio server /home/shared
+     $ minio gateway s3
 ```
 
 ## Assumptions
+
 - Disk cache size defaults to 80% of your drive capacity.
 - The cache drives are required to be a filesystem mount point with [`atime`](http://kerolasa.github.io/filetimes.html) support to be enabled on the drive. Alternatively writable directories with atime support can be specified in MINIO_CACHE_DRIVES
 - Expiration of each cached entry takes user provided expiry as a hint, and defaults to 90 days if not provided.
@@ -34,6 +35,7 @@ minio server -h
 - An object is only cached when drive has sufficient disk space.
 
 ## Behavior
+
 Disk caching caches objects for **downloaded** objects i.e
 
 - Caches new objects for entries not found in cache while downloading. Otherwise serves from the cache.
@@ -50,9 +52,10 @@ master key to automatically encrypt all cached content.
 > NOTE: Expiration happens automatically based on the configured interval as explained above, frequently accessed objects stay alive in cache for a significantly longer time.
 
 ### Crash Recovery
-Upon restart of minio server after a running minio process is killed or crashes, disk caching resumes automatically. The garbage collection cycle resumes and any previously cached entries are served from cache.
+
+Upon restart of minio gateway after a running minio process is killed or crashes, disk caching resumes automatically. The garbage collection cycle resumes and any previously cached entries are served from cache.
 
 ## Limits
+
 - Bucket policies are not cached, so anonymous operations are not supported when backend is offline.
 - Objects are distributed using deterministic hashing among the list of configured cache drives. If one or more drives go offline, or cache drive configuration is altered in any way, performance may degrade to a linear lookup time depending on the number of disks in cache.
-

docs/disk-caching/README.md

@@ -8,42 +8,29 @@ Disk caching feature here refers to the use of caching disks to store content cl
 ## Get started
 
 ### 1. Prerequisites
+
 Install MinIO - [MinIO Quickstart Guide](https://docs.min.io/docs/minio-quickstart-guide).
 
-### 2. Run MinIO with cache
-Disk caching can be enabled by updating the `cache` config settings for MinIO server. Config `cache` settings takes the mounted drive(s) or directory paths, cache expiry duration (in days) and any wildcard patterns to exclude from being cached.
+### 2. Run MinIO gateway with cache
 
-```json
-"cache": {
-	"drives": ["/mnt/drive1", "/mnt/drive2", "/mnt/drive3"],
-	"expiry": 90,
-	"exclude": ["*.pdf","mybucket/*"],
-	"maxuse" : 70,
-},
-```
+Disk caching can be enabled by setting the `cache` environment variables for MinIO gateway . `cache` environment variables takes the mounted drive(s) or directory paths, cache expiry duration (in days) and any wildcard patterns to exclude from being cached.
 
-To update the configuration, use `mc admin config get` command to get the current configuration file for the minio cluster in json format, and save it locally.
-```sh
-$ mc admin config get myminio/ > /tmp/myconfig
-```
-After updating the cache configuration in /tmp/myconfig , use `mc admin config set` command to update the configuration for the cluster.Restart the MinIO server to put the changes into effect.
-```sh
-$ mc admin config set myminio < /tmp/myconfig
-```
-The cache settings may also be set through environment variables. When set, environment variables override any `cache` config settings for MinIO server. Following example uses `/mnt/drive1`, `/mnt/drive2` ,`/mnt/cache1` ... `/mnt/cache3` for caching, with expiry up to 90 days while excluding all objects under bucket `mybucket` and all objects with '.pdf' as extension while starting a standalone erasure coded setup. Cache max usage is restricted to 80% of disk capacity in this example.
+Following example uses `/mnt/drive1`, `/mnt/drive2` ,`/mnt/cache1` ... `/mnt/cache3` for caching, with expiry up to 90 days while excluding all objects under bucket `mybucket` and all objects with '.pdf' as extension while starting a s3 gateway setup. Cache max usage is restricted to 80% of disk capacity in this example.
 
 ```bash
 export MINIO_CACHE_DRIVES="/mnt/drive1;/mnt/drive2;/mnt/cache{1...3}"
 export MINIO_CACHE_EXPIRY=90
 export MINIO_CACHE_EXCLUDE="*.pdf;mybucket/*"
 export MINIO_CACHE_MAXUSE=80
-minio server /export{1...24}
+minio gateway s3
 ```
 
 ### 3. Test your setup
-To test this setup, access the MinIO server via browser or [`mc`](https://docs.min.io/docs/minio-client-quickstart-guide). You’ll see the uploaded files are accessible from the all the MinIO endpoints.
+
+To test this setup, access the MinIO gateway via browser or [`mc`](https://docs.min.io/docs/minio-client-quickstart-guide). You’ll see the uploaded files are accessible from all the MinIO endpoints.
 
 # Explore Further
+
 - [Disk cache design](https://github.com/minio/minio/blob/master/docs/disk-caching/DESIGN.md)
 - [Use `mc` with MinIO Server](https://docs.min.io/docs/minio-client-quickstart-guide)
 - [Use `aws-cli` with MinIO Server](https://docs.min.io/docs/aws-cli-with-minio)