Viveik McCarey

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A Linux container is a set of processes that is separated from the rest of the system. To the end-user, a Linux container functions as a virtual machine, but it’s much more lightweight. You don’t have the overhead of running an additional Linux kernel, and the containers don’t require any CPU hardware virtualization support. This means you can create more containers than virtual machines on the same server.

Imagine that you have a server that should run multiple web sites for your customers. On the one hand, each web site could be a virtual host/server block of the same instance of the Apache or Nginx web server. On the other hand, when using virtual machines, you would create a separate nested virtual machine for each website. Linux containers sit somewhere between virtual hosts and virtual machines.

LXD lets you create and manage these containers. LXD provides a hypervisor service to manage the entire life cycle of containers. In this tutorial, you’ll configure LXD and use it to run Nginx in a container. You’ll then route traffic from the internet to the container to make a sample web page accessible.

To complete this tutorial, you’ll need the following:

Follow the rest of this tutorial to use LXD from the snap package in Ubuntu 20.04. If, however, you want to use the LXD deb package, see our tutorial How To Install and Use LXD on Ubuntu 18.04.

Before you configure and run LXD, you will prepare your server’s environment. This involves adding your sudo user to the lxd group and configuring your storage backend.

When setting up your non-root account, add them to the lxd group using the following command. The adduser command takes as arguments the user account and the Unix group in order to add the user account into the existing Unix group:

Now apply the new membership:

Enter your password and press ENTER.

Finally, confirm that your user is now added to the lxd group:

You will receive an output like this:

Now you are ready to continue configuring LXD.

To begin, you will configure the storage backend.

The recommended storage backend for LXD when you run it on Ubuntu is the ZFS filesystem. ZFS also works very well with DigitalOcean Block Storage. To enable ZFS support in LXD, first update your package list and then install the zfsutils-linux auxiliary package:

We are almost ready to run the LXD initialization script.

Before you do, you must identify and take a note of the device name for your block storage.

To do so, use ls to check the /dev/disk/by-id/ directory:

In this specific example, the full path of the device name is /dev/disk/by-id/scsi-0DO_Volume_volume-fra1-0:

Note down the full file path for your storage device. You will use it in the following step when you configure LXD.

LXD is available as a snap package in Ubuntu 20.04. It comes pre-installed, but you must configure it.

First, verify that the LXD snap package is installed. The command snap list shows installed snap packages:

Ubuntu 20.04 preinstalls LXD 4.0.3, and it is tracking the 4.0/stable channel. LXD 4.0 is supported for five years (until the year 2025). It will only receive security updates:

To find more information about the LXD installed snap package, run snap info lxd. You will be able to see the available versions, including when the package was last updated.

You will now configure LXD.

Start the LXD initialization process using the sudo lxd init command:

First, the program will ask if you want to enable LXD clustering. For the purposes of this tutorial, press ENTER to accept the default no, or type no and then press ENTER. LXD clustering is an advanced topic that enables high availability for your LXD setup and requires at least three LXD servers running in a cluster:

The next six prompts deal with the storage pool. Give the following responses:

Your answers will look like the following:

You have now configured the storage backend for LXD. Continuing with LXD’s init script, you will now configure some networking options.

LXD now asks whether you want to connect to a MAAS (Metal As A Server) server. MAAS is software that makes a bare-metal server appear as, and be handled as if, a virtual machine.

We are running LXD in standalone mode, therefore accept the default and answer no:

You are then asked to configure a network bridge for LXD containers. This enables the following features:

When asked to create a new local network bridge, choose yes:

Then accept the default name, lxdbr0:

Accept the automated selection of private IP address range for the bridge:

Finally, LXD asks the following miscellaneous questions:

When asked if you want to manage LXD over the network, press ENTER or answer no:

When asked if you want to update stale container images automatically, press ENTER or answer yes:

When asked if you want to view and keep the YAML configuration you just created, answer yes if you do. Otherwise, you press ENTER or answer no:

A script will run in the background. It is normal no to receive any output.

You have now configured your network and storage options for LXD. Next you will create your first LXD container.

Now that you have successfully configured LXD, you are ready to create and manage your first container. In LXD, you manage containers using the lxc command followed by an action, such as list, launch, start, stop and delete.

Use lxc list to view the available installed containers:

Since this is the first time that the lxc command communicates with the LXD hypervisor, it shows some information about how to launch a container. Finally, the command shows an empty list of containers. This is expected because we haven’t created any yet:

Now create a container that runs Nginx. To do so, first use the lxc launch command to create and start an Ubuntu 18.04 container named webserver.

Create the webserver container. The 18.04 in ubuntu:18.04 is a shortcut for Ubuntu 18.04. ubuntu: is the identifier for the preconfigured repository of LXD images. You could also use ubuntu:bionic for the image name:

Because this is the first time you’ve created a container, this command downloads the container image from the internet and caches it. You’ll see this output once your new container finishes downloading:

With the webserver container started, use the lxc list command to show information about it. We added --columns ns4 in order to show only the columns for name, state and IPv4 address. The default lxc list command shows three more columns: the IPv6 address, whether the container is persistent or ephemeral, and whether there are snapshots available for each container:

The output shows a table with the name of each container, its current state, its IP address, and its type:

LXD’s DHCP server provides this IP address and in most cases it will remain the same even if the server is rebooted. However, in the following steps you will create iptables rules to forward connections from the internet to the container. Therefore, you should instruct LXD’s DHCP server to always give the same IP address to the container.

The following set of commands will configure the container to obtain a static IP assignment. First, you will override the network configuration for the eth0 device that is inherited from the default LXD profile. This allows you to set a static IP address, which ensures proper communication of web traffic into and out of the container.

Specifically, lxc config device is a command that performs the config action to configure a device. The first line has the sub-action override to override the device eth0 from the container webserver. The second line has the sub-action to set the ipv4.address field of the eth0 device of the webserver container to the IP address that was given by the DHCP server in the beginning.

Run the first config command:

You will receive an output like this:

Now set the static IP:

If the command is successful, you will receive no output.

Restart the container:

Now check the status of the container:

You should see that the container is RUNNING and the IPV4 address is your static address.

You are ready to install and configure Nginx inside the container.

In this step you will connect to the webserver container and configure the web server.

Connect to the container with lxc shell command, which takes the name of the container and starts a shell inside the container:

Once inside the container, your shell prompt will look like the following:

This shell, even if it is a root shell, is limited to the container. Anything that you run in this shell stays in the container and cannot escape to the host server.

Once inside your container, update the package list and install Nginx:

With Nginx installed, you will now edit the default Nginx web page. Specifically, you will add two lines of text so that it is clear that this site is hosted inside the webserver container.

Using nano or your preferred editor, open the file /var/www/html/index.nginx-debian.html:

Add the two highlighted phrases to the file:

You have edited the file in two places and specifically added the text on LXD container webserver. Save the file and exit your text editor.

Now log out of the container:

Once the server’s default prompt returns, use curl to test that the web server in the container is working. To do this, you’ll need the IP address of the web container, which you found using the lxc list command earlier.

Use curl to test your web server:

You will receive the Nginx default HTML welcome page as output. Note that it includes your edits:

The web server is working but you can only access it while on the host using the private IP. In the next step, you will route external requests to this container so the world can access your web site through the internet.

Now that you have configured Nginx, it’s time to connect the webserver container to the internet. To begin, you need to set up the server to forward any connections that it may receive on port 80 to the webserver container. To do this, you’ll create an iptables rule to forward network connections. You can learn more about IPTables in our tutorials, How the IPtables Firewall Works and IPtables Essentials: Common Firewall Rules and Commands.

This iptables command requires two IP addresses: the public IP address of the server (your_server_ip) and the private IP address of the webserver container (your_webserver_container_ip), which you can obtain using the lxc list command.

Execute this command to create a new IPtables rule:

Let’s study that command:

Now list your IPTables rules:

You’ll see output like this:

Now test that the webserver is accessible from the internet

Use the curl command from your local machine to test the connections:

You’ll see the headers followed by the contents of the web page you created in the container:

This confirms that the requests are going to the container.

Finally, you will save the firewall rule so that it reapplies after a reboot.

To do so, first install the iptables-persistent package:

When installing the package, the application will prompt you to save the current firewall rules. Accept and save all current rules.

When you reboot your machine, the firewall rule will load. In addition, the Nginx service in your LXD container will automatically restart.

You’ve successfully configured LXD. In the final step you will learn how to stop and destroy the service.

You may decide that you want to take down the container and delete it. In this step you will stop and remove your container.

First, stop the container:

Use the lxc list command to verify the status:

You will see that the container’s state reads STOPPED:

To remove the container, use lxc delete:

Running lxc list again shows that there’s no container running:

The command will output the following:

Use the lxc help command to see additional options.

To remove the firewall rule that routes traffic to the container, first locate the rule in the list of rules with this command, which associates a line number with each rule:

You’ll see your rule, prefixed with a line number, like this:

Use that line number to remove the rule:

List the rules again to ensure removal:

The rule is removed:

Now save the changes so that the rule doesn’t come back when you restart your server:

You can now bring up another container with your own settings and add a new firewall rule to forward traffic to it.

In this tutorial, you installed and configured LXD. You then created a website using Nginx running inside an LXD container and made it publicly available us IPtables.

From here, you could configure more websites, each confined to its own container, and use a reverse proxy to direct traffic to the appropriate container. The tutorial How to Host Multiple Web Sites with Nginx and HAProxy Using LXD on Ubuntu 16.04 walks you through that setup.

See the LXD reference documentation for more information on how to use LXD.

To practice with LXD, you can try LXD online and follow the web-based tutorial.

• First eat your mango and save the pit.
• Cut the pit apart and pull out the seed.
• The seed is ready to be planted.
• After ten days to two weeks you should see a shoot start to grow.
• This mango seedling is about six months old.
• The mango plant at about 14 months old.

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