install: Improve snap documentation

Improve snap documentation, document how to install
kata 1.x and 2.x, how to configure them and their integration
with container engines.

fixes #1138

Signed-off-by: Julio Montes <julio.montes@intel.com>

docs/install/snap-installation-guide.md

@@ -1,13 +1,123 @@
-# Install Kata Containers from `snapcraft.io`
+# Kata Containers snap package
+
+* [Install Kata Containers](#install-kata-containers)
+* [Configure Kata Containers](#configure-kata-containers)
+* [Integration with non-compatible shim v2 Container Engines](#integration-with-non-compatible-shim-v2-container-engines)
+    * [Integration with Docker](#integration-with-docker)
+    * [Integration with Podman](#integration-with-podman)
+* [Integration with shim v2 Container Engines](#integration-with-shim-v2-container-engines)
+* [Remove Kata Containers snap package](#remove-kata-containers-snap-package)
+
+
+## Install Kata Containers
 
 Kata Containers can be installed in any Linux distribution that supports
 [snapd](https://docs.snapcraft.io/installing-snapd).
 
-Run the following command to install Kata Containers:
+> NOTE: From Kata Containers 2.x, only the [Containerd Runtime V2 (Shim API)](https://github.com/containerd/containerd/tree/master/runtime/v2)
+> is supported, note that some container engines (`docker`, `podman`, etc) may not
+> be able to run Kata Containers 2.x.
 
-   ```bash
-   $ sudo snap install kata-containers --classic
-   ```
+Kata Containers 1.x is released through the *stable* channel while Kata Containers
+2.x is available in the *candidate* channel.
 
-For further information on integrating and configuring the `snap` Kata Containers install,
-refer to the [Kata Containers packaging `snap` documentation](https://github.com/kata-containers/packaging/blob/master/snap/README.md#configure-kata-containers).
+Run the following command to install **Kata Containers 1.x**:
+
+```sh
+$ sudo snap install kata-containers --classic
+```
+
+Run the following command to install **Kata Containers 2.x**:
+
+```sh
+$ sudo snap install kata-containers --candidate --classic
+```
+
+## Configure Kata Containers
+
+By default Kata Containers snap image is mounted at `/snap/kata-containers` as a
+read-only file system, therefore default configuration file can not be edited.
+Fortunately Kata Containers supports loading a configuration file from another
+path than the default.
+
+```sh
+$ sudo mkdir -p /etc/kata-containers
+$ sudo cp /snap/kata-containers/current/usr/share/defaults/kata-containers/configuration.toml /etc/kata-containers/
+$ $EDITOR /etc/kata-containers/configuration.toml
+```
+
+## Integration with non-compatible shim v2 Container Engines
+
+At the time of writing this document, `docker` and `podman` **do not support Kata
+Containers 2.x, therefore Kata Containers 1.x must be used instead.**
+
+The path to the runtime provided by the Kata Containers 1.x snap package is
+`/snap/bin/kata-containers.runtime`, it should be used to run Kata Containers 1.x.
+
+### Integration with Docker
+
+`/etc/docker/daemon.json` is the configuration file for `docker`, use the
+following configuration to add a new runtime (`kata`) to `docker`.
+
+```json
+{
+  "runtimes": {
+    "kata": {
+      "path": "/snap/bin/kata-containers.runtime"
+    }
+  }
+}
+```
+
+Once the above configuration has been applied, use the
+following commands to restart `docker` and run Kata Containers 1.x.
+
+```sh
+$ sudo systemctl restart docker
+$ docker run -ti --runtime kata busybox sh
+```
+
+### Integration with Podman
+
+`/usr/share/containers/containers.conf` is the configuration file for `podman`,
+add the following configuration in the `[engine.runtimes]` section.
+
+```toml
+kata = [
+   "/snap/bin/kata-containers.runtime"
+]
+```
+
+Once the above configuration has been applied, use the following command to run
+Kata Containers 1.x with `podman`
+
+```sh
+$ sudo podman run -ti --runtime kata docker.io/library/busybox sh
+```
+
+## Integration with shim v2 Container Engines
+
+The Container engine daemon (`cri-o`, `containerd`, etc) needs to be able to find the
+`containerd-shim-kata-v2` binary to allow Kata Containers to be created.
+Run the following command to create a symbolic link to the shim v2 binary.
+
+```sh
+$ sudo ln -sf /snap/kata-containers/current/usr/bin/containerd-shim-kata-v2 /usr/local/bin/containerd-shim-kata-v2
+```
+
+Once the symbolic link has been created and the engine daemon configured, `io.containerd.kata.v2`
+can be used as runtime.
+
+Read the following documents to know how to run Kata Containers 2.x with `containerd`.
+
+* [How to use Kata Containers and Containerd](https://github.com/kata-containers/kata-containers/blob/2.0-dev/docs/how-to/containerd-kata.md)
+* [Install Kata Containers with containerd](https://github.com/kata-containers/kata-containers/blob/2.0-dev/docs/install/container-manager/containerd/containerd-install.md)
+
+
+## Remove Kata Containers snap package
+
+Run the following command to remove the Kata Containers snap:
+
+```sh
+$ sudo snap remove kata-containers
+```