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       .remark-slide-content h1 { font-size: 50px; }
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+      .footnote {
+        position: absolute;
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+      }
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@@ -4772,6 +4776,245 @@ class: secrets
 
 ---
 
+class: namespaces
+name: namespaces
+
+# Improving isolation with User Namespaces
+
+- *Namespaces* are kernel mechanisms to compartimetalize the system
+
+- There are different kind of namespaces: `pid`, `net`, `mnt`, `ipc`, `uts`, and `user`
+
+- For a primer, see "Anatomy of a Container"
+  ([video](https://www.youtube.com/watch?v=sK5i-N34im8))
+  ([slides](https://www.slideshare.net/jpetazzo/cgroups-namespaces-and-beyond-what-are-containers-made-from-dockercon-europe-2015))
+
+- The *user namespace* allows to map UIDs between the containers and the host
+
+- As a result, `root` in a container can map to a non-privileged user on the host
+
+Note: even without user namespaces, `root` in a container cannot go wild on the host.
+<br/>
+It is mediated by capabilities, cgroups, namespaces, seccomp, LSMs...
+
+---
+
+class: namespaces
+
+## User Namespaces in Docker
+
+- Optional feature added in Docker Engine 1.10
+
+- Not enabled by default
+
+- Has to be enabled at Engine startup, and affects all containers
+
+- When enabled, `UID:GID` in containers are mapped to a different range on the host
+
+- Safer than switching to a non-root user (with `-u` or `USER`) in the container
+  <br/>
+  (Since with user namespaces, root escalation maps to a non-privileged user)
+
+- Can be selectively disabled per container by starting them with `--userns=host`
+
+---
+
+class: namespaces
+
+## User Namespaces Caveats
+
+When user namespaces are enabled, containers cannot:
+
+- Use the host's network namespace (with `docker run --network=host`)
+
+- Use the host's PID namespace (with `docker run --pid=host`)
+
+- Run in privileged mode (with `docker run --privileged`)
+
+... Unless user namespaces are disabled for the container, with flag `--userns=host`
+
+External volume and graph drivers that don't support user mapping might not work.
+
+All containers are currently mapped to the same UID:GID range.
+
+Some of these limitations might be lifted in the future!
+
+---
+
+class: namespaces
+
+## Filesystem ownership details
+
+When enabling user namespaces:
+
+- the UID:GID on disk (in the images and containers) has to match the *mapped* UID:GID
+
+- existing images and containers cannot work (their UID:GID would have to be changed)
+
+For practical reasons, when enabling user namespaces, the Docker Engine places containers and images (and everything else) in a different directory.
+
+As a resut, if you enable user namespaces on an existing installation:
+
+-  all containers and images (and e.g. Swarm data) disappear
+
+- *if a node is a member of a Swarm, it is then kicked out of the Swarm*
+
+-  everything will re-appear if you disable user namespaces again
+
+---
+
+class: namespaces
+
+## Picking a node
+
+- We will select a node where we will enable user namespaces
+
+- This node will have to be re-added to the Swarm
+
+- All containers and services running on this node will be rescheduled
+
+- Let's make sure that we do not pick the node running the registry!
+
+.exercise[
+
+- Check on which node the registry is running:
+  ```bash
+  docker service ps registry
+  ```
+
+]
+
+Pick any other node (noted `nodeX` in the next slides).
+
+---
+
+class: namespaces
+
+## Logging into the right Engine
+
+.exercise[
+
+- Log into the right node:
+  ```bash
+  ssh node`X`
+  ```
+
+]
+
+---
+
+class: namespaces
+
+## Configuring the Engine
+
+.exercise[
+
+- Create a configuration file for the Engine:
+  ```bash
+  echo '{"userns-remap": "default"}' | sudo tee /etc/docker/daemon.json
+  ```
+
+- Restart the Engine:
+  ```bash
+  kill $(pidof dockerd)
+  ```
+
+]
+
+---
+
+class: namespaces 
+
+## Checking that User Namespaces are enabled
+
+.exercise[
+  - Notice the new Docker path:
+  ```bash
+  docker info | grep var/lib
+  ```
+
+  - Notice the new UID:GID permissions:
+  ```bash
+  sudo ls -l /var/lib/docker
+  ```
+
+]
+
+You should see a line like the following:
+```
+drwx------ 11 296608 296608 4096 Aug  3 05:11 296608.296608
+```
+
+---
+
+class: namespaces
+
+## Add the node back to the Swarm
+
+.exercise[
+
+- Get our manager token from another node:
+  ```bash
+  ssh node`Y` docker swarm join-token manager
+  ```
+
+- Copy-paste the join command to the node
+
+]
+
+---
+
+class: namespaces
+
+## Check the new UID:GID
+
+.exercise[
+
+- Run a background container on the node:
+  ```bash
+  docker run -d --name lockdown alpine sleep 1000000
+  ```
+
+- Look at the processes in this container:
+  ```bash
+  docker top lockdown
+  ps faux
+  ```
+
+]
+
+---
+
+class: namespaces
+
+## Comparing on-disk ownership with/without User Namespaces
+
+.exercise[
+
+- Compare the output of the two following commands:
+  ```bash
+  docker run alpine ls -l /
+  docker run --userns=host alpine ls -l /
+  ```
+
+]
+
+--
+
+class: namespaces
+
+In the first case, it looks like things belong to `root:root`.
+
+In the second case, we will see the "real" (on-disk) ownership.
+
+--
+
+class: namespaces
+
+Remember to get back to `node1` when finished!
+
+---
+
 ## A reminder about *scope*
 
 - Out of the box, Docker API access is "all or nothing"