engine: configure registry push/pull with containerd

Signed-off-by: David Karlsson <35727626+dvdksn@users.noreply.github.com>

Author: dvdksn

content/manuals/engine/daemon/containerd.md

@@ -0,0 +1,135 @@
+---
+title: Registry host configuration
+description: Configure per-registry behavior for Docker Engine using hosts.toml files
+keywords: containerd, registry, hosts, push, pull, mirror, configuration, daemon
+weight: 25
+---
+
+When using the [containerd image store](/manuals/engine/storage/containerd.md),
+you can configure per-registry behavior using `hosts.toml` files. This lets
+you restrict push or pull access, redirect traffic to a mirror, or customize
+TLS settings on a per-registry basis.
+
+## Configuration directory
+
+Docker Engine reads registry host configuration from the following directory:
+
+| Setup         | Directory                   |
+| ------------- | --------------------------- |
+| Regular       | `/etc/docker/certs.d/`      |
+| Rootless mode | `~/.config/docker/certs.d/` |
+
+Create a subdirectory for each registry you want to configure. The directory
+name must match the registry host as it appears in image references:
+
+| Image reference                         | Directory                    |
+| --------------------------------------- | ---------------------------- |
+| `docker.io/myorg/myimage:latest`        | `docker.io/`                 |
+| `registry.example.com/myimage:latest`   | `registry.example.com/`      |
+| `registry.example.com:5000/myimage:tag` | `registry.example.com:5000/` |
+
+Each directory contains a `hosts.toml` file:
+
+```text
+/etc/docker/certs.d/
+├── docker.io/
+│   └── hosts.toml
+├── registry.example.com/
+│   └── hosts.toml
+└── registry.example.com:5000/
+    └── hosts.toml
+```
+
+Changes to `hosts.toml` files take effect immediately, without restarting
+Docker.
+
+## hosts.toml format
+
+Each `hosts.toml` file configures the behavior for one registry. The `server`
+field sets the upstream registry URL. The `[host]` section configures specific
+endpoints, including what operations they're allowed to perform using the
+`capabilities` field.
+
+Valid capabilities are:
+
+| Capability | Description          |
+| ---------- | -------------------- |
+| `pull`     | Allow pulling images |
+| `resolve`  | Allow tag resolution |
+| `push`     | Allow pushing images |
+
+## Examples
+
+### Disable push to a registry
+
+To prevent Docker from pushing images to a specific registry, omit `push` from
+the capabilities:
+
+```toml {title="/etc/docker/certs.d/docker.io/hosts.toml"}
+server = "https://registry-1.docker.io"
+
+[host."https://registry-1.docker.io"]
+  capabilities = ["pull", "resolve"]
+```
+
+With this configuration, `docker pull` from Docker Hub works normally, but
+`docker push` to Docker Hub returns an error.
+
+### Redirect pulls to a mirror
+
+To route pull traffic through a registry mirror:
+
+```toml {title="/etc/docker/certs.d/docker.io/hosts.toml"}
+server = "https://registry-1.docker.io"
+
+[host."https://mirror.example.com"]
+  capabilities = ["pull", "resolve"]
+
+[host."https://registry-1.docker.io"]
+  capabilities = ["pull", "resolve", "push"]
+```
+
+Docker tries the mirror first for pulls, and falls back to Docker Hub if the
+mirror doesn't have the image. Pushes always go to Docker Hub directly.
+
+### Internal registry only
+
+To restrict Docker to only push and pull from an internal registry, and block
+access to all public registries:
+
+```toml {title="/etc/docker/certs.d/docker.io/hosts.toml"}
+server = "https://registry-1.docker.io"
+
+[host."https://registry-1.docker.io"]
+  capabilities = []
+```
+
+With no capabilities, all operations to that registry fail.
+
+> [!NOTE]
+> This configuration controls behavior at the daemon level, not as a security
+> boundary. Builds, containers, and other mechanisms can still interact with
+> registries. For strict registry access control, consider
+> [Registry Access Management](/manuals/enterprise/security/hardened-desktop/registry-access-management.md)
+> in Docker Business.
+
+## Relation to daemon.json registry settings
+
+Docker daemon also supports registry configuration through `daemon.json` options
+like `insecure-registries` and `registry-mirrors`. These settings interact with
+`hosts.toml` as follows:
+
+- If a `hosts.toml` file configures **two or more** endpoints for a registry
+  (such as a mirror and an upstream fallback), the daemon.json settings for that
+  registry are **ignored**. The `hosts.toml` configuration takes full control.
+- If `hosts.toml` is absent or configures only a single endpoint, the
+  daemon.json settings are applied on top.
+
+If you're using `hosts.toml` to configure mirrors for a registry, include all
+TLS and authentication settings in the `hosts.toml` file rather than relying on
+`insecure-registries` in `daemon.json`.
+
+## Reference
+
+For the full `hosts.toml` specification, see the
+[containerd registry hosts documentation](https://github.com/containerd/containerd/blob/main/docs/hosts.md).