docker: added distroless image

docker/README.md

@@ -12,6 +12,7 @@ SFTPGo provides an official Docker image, it is available on both [Docker Hub](h
 - [edge-alpine](../Dockerfile.alpine)
 - [edge-slim](../Dockerfile)
 - [edge-alpine-slim](../Dockerfile.alpine)
+- [edge-distroless-slim](../Dockerfile.distroless)
 
 ## How to use the SFTPGo image
 
@@ -87,6 +88,8 @@ The logs are available through Docker's container log:
 docker logs some-sftpgo
 ```
 
+**Note:** [distroless](../Dockerfile.distroless) image contains only application and its runtime dependencies. Shell access is not available on this image.
+
 ### Where to Store Data
 
 Important note: There are several ways to store data used by applications that run in Docker containers. We encourage users of the SFTPGo images to familiarize themselves with the options available, including:
@@ -166,6 +169,8 @@ RUN chown -R 1100:1100 /etc/sftpgo && chown 1100:1100 /var/lib/sftpgo /srv/sftpg
 USER 1100:1100
 ```
 
+**Note:** the above Dockerfile will not work for [distroless](../Dockerfile.distroless) image since the `chown` command is not available there.
+
 ## Image Variants
 
 The `sftpgo` images comes in many flavors, each designed for a specific use case. The `edge` and `edge-alpine`tags are updated after each new commit.
@@ -180,6 +185,14 @@ This image is based on the popular [Alpine Linux project](https://alpinelinux.or
 
 This variant is highly recommended when final image size being as small as possible is desired. The main caveat to note is that it does use [musl libc](https://musl.libc.org/) instead of [glibc and friends](https://www.etalabs.net/compare_libcs.html), so certain software might run into issues depending on the depth of their libc requirements. However, most software doesn't have an issue with this, so this variant is usually a very safe choice. See [this Hacker News comment thread](https://news.ycombinator.com/item?id=10782897) for more discussion of the issues that might arise and some pro/con comparisons of using Alpine-based images.
 
+### `sftpgo:<version>-distroless`
+
+This image is based on the popular [Distroless project](https://github.com/GoogleContainerTools/distroless). We use the latest Debian based distroless image as base.
+
+Distroless image contains only application and its runtime dependencies and so it doesn't allow shell access (no shell is installed).
+SQLite support is disabled since it requires CGO and so a C runtime. We use a statically linked SFTPGo binary here.
+The default data-provider is `bolt`, all the supported data providers expect `sqlite` work.
+
 ### `sftpgo:<suite>-slim`
 
 These tags provide a slimmer image that does not include the optional `git` and `rsync` dependencies.