Expose LXC/LXD Container Ports to Public

LXC/LXD is lightweight OS-level virtualization on Linux, much like OpenVZ. It was used by early version of Docker. The benefit of using LXC/LXD is when you need a virtualization but also need fast startup and near-baremetal performance (especially compared to full-virtualization like KVM or VirtualBox). The difference between Docker and LXC is which level they are targeting, Docker is more for application deployment, where LXC is machine level. LXD adds REST API for LXC. Other main difference between LXC and Docker is that Docker has a copy-on-write file system built-in. To start using LXD, just install and run:

sudo apt install lxc lxd libvirt-bin zfsutils-linux
sudo lxd init

# there would be questions to be answered like these:
Would you like to use LXD clustering? (yes/no) [default=no]: 
Do you want to configure a new storage pool? (yes/no) [default=yes]: 
Name of the new storage pool [default=default]: 
Name of the storage backend to use (dir, lvm, zfs) [default=zfs]: 
Create a new ZFS pool? (yes/no) [default=yes]: 
Would you like to use an existing block device? (yes/no) [default=no]: 
Size in GB of the new loop device (1GB minimum) [default=100GB]:    
Would you like to connect to a MAAS server? (yes/no) [default=no]: 
Would you like to create a new local network bridge? (yes/no) [default=yes]: 
What should the new bridge be called? [default=lxdbr0]: 
What IPv4 address should be used? (CIDR subnet notation, “auto” or “none”) [default=auto]: 
What IPv6 address should be used? (CIDR subnet notation, “auto” or “none”) [default=auto]: 
Would you like LXD to be available over the network? (yes/no) [default=no]: yes
Address to bind LXD to (not including port) [default=all]: 127.0.0.1
Port to bind LXD to [default=8443]: 
Trust password for new clients: 
Again: 
Would you like stale cached images to be updated automatically? (yes/no) [default=yes] 
Would you like a YAML "lxd init" preseed to be printed? (yes/no) [default=no]:

# cache one and run one container, but this will only shown on lxc-ls
sudo lxc-create -t download -n container1 -- --dist ubuntu --release bionic --arch amd64
sudo lxc-start --name container1 --daemon
sudo lxc-info --name container1
sudo lxc-stop --name container1
sudo lxc-destroy --name container1

# or run one container
lxc launch ubuntu:18.04 container1

# run command inside, enable ssh with password, change the root password
lxc exec container1 bash
echo '
PermitRootLogin yes
PasswordAuthentication yes
' > /etc/ssh/sshd_config
systemctl restart ssh
passwd

Then you'll need to expose (or port forward) from outside to your container:

# get ip from your container
lxc list
+------------+---------+-----------------------+------------+-----------+
|    NAME    |  STATE  |         IPV4          |    TYPE    | SNAPSHOTS |
+------------+---------+-----------------------+------------+-----------+
| container1 | RUNNING | 10.123.126.200 (eth0) | PERSISTENT | 0         |
+------------+---------+-----------------------+------------+-----------+

# forward real port 2200 to container's port 22 and vice versa
iptables -A FORWARD -i eth0 -j DROP
iptables -A FORWARD -i lxdbr0 -m state --state NEW,INVALID -j DROP
iptables -A FORWARD -i eth0 -d 10.123.126.200 -p tcp --dport 2200 -j ACCEPT
iptables -t nat -A PREROUTING -p tcp --dport 2200 -j DNAT --to 10.123.126.200:22

You can test whether the port forwarding and ssh works using these command from another computer:

ssh -o PreferredAuthentications=keyboard-interactive,password -o PubkeyAuthentication=no root:@thePublicIpAddress -p 2200

If you need to expose more ports, for example container's 80 to real's 8080 for example, you can add the rules like this:

iptables -A FORWARD -i eth0 -d 10.123.126.200 -p tcp --dport 8080 -j ACCEPT
iptables -t nat -A PREROUTING -p tcp --dport 8080 -j DNAT --to 10.123.126.200:80

But for this case, I think it's better to use a reverse proxy instead.

Here's the performance difference between baremetal machine and LXC?

CPU model:  Intel(R) Xeon(R) CPU E5-2630 v4 @ 2.20GHz 
Number of cores: 8
CPU frequency:  2199.996 MHz
Total amount of RAM: 30151 MB
Total amount of swap:  MB
System uptime:   147 days, 20:48,    
I/O speed:  132 MB/s
Bzip 25MB: 8.01s
Download 100MB file: 69.2MB/s

I/O speed(1st run)   : 127 MB/s
I/O speed(2nd run)   : 107 MB/s
I/O speed(3rd run)   : 107 MB/s
Average I/O speed    : 113.7 MB/s

LXC (because the write not yet committed?):

CPU model:  Intel(R) Xeon(R) CPU E5-2630 v4 @ 2.20GHz 
Number of cores: 8
CPU frequency:  2199.996 MHz
Total amount of RAM: 30151 MB
Total amount of swap:  MB
System uptime:   20 min,    
I/O speed:  451 MB/s
Bzip 25MB: 9.40s
Download 100MB file: 63.7MB/s

I/O speed(1st run)   : 925 MB/s
I/O speed(2nd run)   : 1.2 GB/s
I/O speed(3rd run)   : 956 MB/s
Average I/O speed    : 1036.6 MB/s