server

A 3-post collection

xhyve: a quick how to

So here we are, xhyve finally usable, so how to use it?

Fetching the source and compiling it

To compile xhyve you need either Xcode or at least the Xcode command line tools from Apple. If you not already have those installed run the following in a Terminal window:

xcode-select --install

Now you're ready to checkout the source code and compile it:

git clone https://github.com/dunkelstern/xhyve.git xhyve
cd xhyve
git checkout sparse-disk-image
make

If everything worked the last lines of the make output should look something like this:

ld xhyve.sym
dsym xhyve.dSYM
strip xhyve

If you want you could install the xhyve binary to /usr/local/bin now or just copy it somewhere where you'll find it:

sudo mkdir -p /usr/local/{bin,share/man/man1}
sudo cp build/xhyve /usr/local/bin/
sudo cp xhyve.1 /usr/local/share/man/man1/

(It will ask for your password when using sudo, if you have Homebrew installed you might skip the sudo)

The first config file

A xhyve config file is a simple shell script, as xhyve takes all configuration in it's command line parameters.

What's possible

The best option to see what xhyve actually can do is the man page, but I will describe the basics to you nonetheless.

Open the man page with man ./xhyve.1 while you're in the source directory or just with man xhyve if you copied the binary and man-page into /usr/local.

So what can xhyve emulate:

ACPI

Command line parameter: -A

This is an option that should be set all the time except if you get weird ACPI related crashes.

Number of CPUs

Command line parameter: -c <number>

How many CPU cores you want to share with the guest operating system, defaults to one, maximum is 16.

Allocated RAM

Command line parameter: -m <number>

Amount of RAM to give to the guest operating system. You may use suffixes like k, m or g for Kilobytes, Megabytes or Gigabytes.

Virtual COM ports

Command line parameter: -l <source-device>,<destination-device>

This maps a virtual COM port (serial port) to a host device.
<source-device> may be either com1 or com2 and <destination-device> may be either stdio (to connect the serial port to the terminal window's console) or any character device in /dev/.

Virtual PCI bus

Command line parameter: -s <slot>,<emulation>,[config]

This is a bit more complex as it defines which hardware is connected to your VM.

<slot> is a number from 0 to 31 that defines the PCI slot.

<emulation> is the device to emulate. xhyve knows the following devices:

  • hostbridge, this is usually needed at slot 0 for most guests
  • virtio-net, a virtual network card
  • virtio-blk, a virtual block device (a disk)
  • ahci-cd, a virtual CD-ROM/DVD-ROM drive
  • ahci-hd, a virtual disk for guests that have no virtio driver
  • uart, a virtual serial port (COM3+)
  • lpc, a PCI to ISA bridge, used for COM1 and COM2

Each of these has a specific configuration that may be set, see the man page for further instructions, an example of the usage follows.

Linux kernel to boot

Command line parameter: -f kexec,<kernel>,<initrd>,<kernel command line>

This essentially specifies which linux kernel to load. The problem with xhyve is that it has no BIOS or EFI emulation, so it loads the Linux kernel directly, this leads to a small inconvenience: We need the Kernel outside of the disk image.

What's needed

So this is all nice and good but which of these command line flags do we really need to get a standard Ubuntu running?

  • -A, for ACPI mode
  • -m 1G, 1GB RAM
  • -s 0,hostbridge -s 31,lpc, basically the minimum PCI config that works
  • -l com1,stdio, map the first serial port to the Terminal window
  • -s 1,ahci-cd,ubuntu-15.10-server-amd64.iso, the CD-ROM with the Ubuntu ISO inserted
  • -s 2,virtio-blk,hdd.img,sectorsize=4096,size=20G,split=1G,sparse, the main disk, 20GB max size, split into 1GB parts, use a sector size of 4096 (best choice for SSDs) and do not eat my harddisk space (sparse)
  • -f kexec,vmlinuz,initrd.gz,"earlyprintk console=ttyS0", load a linux kernel from the files vmlinuz and initrd.gz the kernel parameters tell Ubuntu to map the console to the first serial port so we can see the boot process in the Terminal.

All in one (save as install.sh):

# Linux
KERNEL="vmlinuz"
INITRD="initrd.gz"
CMDLINE="earlyprintk=serial console=ttyS0"

# Guest Config
MEM="-m 1G"
IMG_CD="-s 1,ahci-cd,ubuntu-15.10-server-amd64.iso"
IMG_HDD="-s 2,virtio-blk,hdd.img,size=20G,split=1G,sparse"
NET="-s 3,virito-net,vmnet0"
PCI_DEV="-s 0:0,hostbridge -s 31,lpc"
LPC_DEV="-l com1,stdio"
ACPI="-A"

# and now run
sudo xhyve $ACPI $MEM $PCI_DEV $LPC_DEV $NET $IMG_CD $IMG_HDD -f kexec,$KERNEL,$INITRD,"$CMDLINE"

As you might have noticed, we run the xhyve binary as root this is because the xhyve binary has to be code signed with an Apple Developer Key or run as root to use the networking infrastructure. Let's just install Ubuntu and think about that later.

Installing ubuntu

As there is no graphical output we have to install Ubuntu Server (as only the Server version has the text-mode installer).

Go get it here: http://www.ubuntu.com/download/server

As you have read in the What's possible section, we need a Linux Kernel outside of our disk images to boot. So let's get one.

Extracting the setup kernel

As the Ubuntu install CD contains all files we need, why not just extract it from the disk image? Well there's one catch: Ubuntu uses a so called Mixed-Mode CD image and Mac OS X doesn't really like to mount such a disk so we have to resort to a small trick, execute the following on a Terminal to get the Kernel:

# create a 2k temporary file filled with zeroes
dd if=/dev/zero bs=2k count=1 of=tmp.iso

# append the ubuntu server image to that
dd if=ubuntu-15.10-server-amd64.iso bs=2k skip=1 >> tmp.iso

# mount it
hdiutil attach tmp.iso

# copy needed files
cp /Volumes/Ubuntu-Server\ 15/install/vmlinuz .
cp /Volumes/Ubuntu-Server\ 15/install/initrd.gz .

# unmount it
hdiutil detach /Volumes/Ubuntu-Server\ 15

You may want to keep tmp.iso or as well delete it as we have what we want. (Thanks to the people at pagetable for this neat trick)

Running the setup

If you saved the All in one script from above, make it executable with chmod a+x install.sh and run it.

If everything worked Ubuntu should boot in your Terminal.
Do not finish the setup yet, as you'll need to do something before:

Extracting the system kernel

When you finished setup you'll need to exchange which Kernel to load. The easiest thing to do that is by opening a console in the ubuntu installer. If it asks you if you want to finish the installation and reboot, don't do that but return to the main installer menu, there's an option Open a console that we need now.

After being dumped into the console make the installed target your change root:

chroot /target
bash
cd /boot

Now open a second Terminal window on your Mac and run the following:

nc -l -p 1234 | tar x

This starts a netcat server that listens on the port 1234 for a connection from the Ubuntu guest and expects to receive a tar file.

Now on the Ubuntu guest execute the following:

tar cv vmlinuz* initrd.img* | nc <ip_of_mac> 1234

If everything worked you should have two files on your Mac:

  • vmlinuz-4.2.0-16-generic
  • initrd.img-4.2.0-16-generic

(The version number may differ)

Now finish the setup and let Ubuntu reboot. Rebooting should exit xhyve and dump you to your Mac console. This is correct!

Boot config

Now copy install.sh to boot.sh and make the following changes:

  • replace the files for INITRD and KERNEL with those you extracted from the VM
  • add root=/dev/vda1 to the Kernel command line after console=ttyS0
  • You may comment out the IMG_CD line

In future, to boot Ubuntu, you'll only need to run boot.sh and it will just work.

xhyve: lightweight vm for Mac OS X

xhyve is a port of bhyve a qemu equivalent for FreeBSD to the Mac OS X Hypervisor framework. This means it has zero dependencies that are not already installed on every Mac that runs at least OS X Yosemite (10.10). The cool thing though is that Mac OS X has full control of the system all the time as no third party kernel driver hijacks the CPU when a VM is running, so the full power management that OS X provides is always in charge of everything. No more battery draining VMs \o/.

xhyve logo

xhyve is Open Source

This is really cool as everyone is able to hack it, so did I. The code is, like every bit of lowlevel C code I saw in my life, a bit complex to read and has not many comments but is very structured so you can easily find what you want to modify and do that.

The project is quite young so don't expect miracles. It has for example no graphics emulation. Running Ubuntu or FreeBSD is reduced to a serial tty and networking. If you want to run a virtual server on your Mac for development purposes it's quite perfect though.

There was one downer that got me: A virtual disk of say 30 GB has a backing file that is exactly 30 GB big even if you only store 400 MB on it. That's bad for everyone running on a SSD where space is limited as of now.

Introducing: Sparse HDD-Images for xhyve

Because the VM code is pretty small (the compiled executable of xhyve is about 230 KB) I though it might be possible for me to change this one last thing that prevented me to use xhyve on my Macbook. It turns out it is really easy to hack the virtual block device subsystem. All disk access code is neatly contained in one file: blockif.c. It is neatly separated from the virtio-block and ahci drivers.

So what I went out to do was three things:

  • Split the big disk image file into multiple segments (as for why read on)
  • Make the disk image segments only store blocks that have actual content in them (vs. storing only zeroes)
  • Make xhyve create the backing image files if they do not exist.

Splitting the disk image into segments

You may ask why, this is rather an optimization for maintaining speed and aid debugging but turned out to have the following advantages:

  • Some file systems may only allow files of a maximum size (prime example: FAT32 only allows 2GB per file)
  • Sparse image lookup tables can be filled with 32 bit values instead of defaulting to 64 bit (which saves 50% space in the lookup tables)
  • Debugging is easier as you may hexdump those smaller files on the terminal instead of loading a multi gigabyte file into the hex editor of your choice
  • Fragmentation of sparse images is reduced somewhat (probably not an issue for SSD backed files)
  • Growing disks is easy: just append a segment
  • Shrinking disks should be possible with help of the guest operating system, if it is able to clear the end of the disk of any data you could just delete a segment.

So splitting was implemented and rather easy to think of, just divide the disk read offset by the segment size and use a modulo operation to get to the in-segment-address. There's one catch: I had to revert from using preadv and pwritev to regular reads and writes. Usually you really want those v functions as they allow executing multiple read and write calls in one system call, thus beeing atomic. But these functions only work with one file descriptor and our reads probably span multiple segments and thus multiple file descriptors.

To make the thing easier and configurable I introduced two additional parameters for the block device configuration:

  • size the size of the backing file for the virtual disk
  • split the segment size. size should be a multiple of split to avoid wasting space.

You may use suffixes like k, m, g like on the RAM settings to avoid calculating the real byte sizes in your head ;)

Be aware: You may convert a disk from plain to split image either by using dd and splitting the image file (exact commands are left as an exercise to the reader) or by setting split to the old size of the image and size to a multiple of split effectively increasing the size of the disk by a multiple of the old size. New segments will be created automatically on next VM start.

Example config

Implementing sparse images

So the last step for making xhyve usable to me: Don't waste my disk space.

I think there are multiple methods for implementing efficient sparse images, I went for the following:

  • Only save sectors that contain actual data and not only zeroes
  • Minimum allocation size is one sector
  • Maintain a lookup table that references where each sector is saved in the image
  • Deallocation of a sector (e.g. overwriting with zeroes) is only handled by a shrink disk tool offline

So how does such a lookup table look?

A sparse disk lookup table is just an array of 32 bit unsigned integers, one for each sector. If you want to read sector 45 you just take the value of array position 45, multiply it by sector size and seek into the image segment to read from that address. Simple, isn't it?

In the current implementation the lookup table is written to a separate file with the extension .lut, all writes to this file are synchronous. The other backing files will be initially created as zero byte length files and when the guest os starts writing data the new sector is appended to the respective segment file and a new offset is written to the lookup table.

The lookup table starts as an array full of UINT32_MAX values (0xffffffff) as this is the marker used to describe that this sector is not yet in the image and thus should be returned as a series of zero values. If a read finds an entry other than that marker the corresponding data is read from the segment file.

All lookup tables for all segment files are appended to the .lut file, so it contains multiple tables, not just one. Positive side of this is that 32 bits of offset data map to a maximum segment size of about just under 4 TB divided by the sector size. If you use an SSD as backing storage you probably should configure your sector size to 4KB as that is the sector size of most SSDs and will result in additional performance. So this will result in a maximum segment size of about 16 PB and I never heard of a Mac that has this much storage. (If yours has please send me a photo)

Writes of new sectors (those appended to the segment file) are synchronous to avoid two sectors with the same address. Other writes are as the user configured them on the command line.

To enable sparse disk images just add sparse as a parameter to your configuration.

Sparse config example

Be aware: You'll have to recreate your disk image to profit of this setting, sparse disks are not compatible with normal disks.

Conclusion

I used this configuration:

-s 4,virtio-blk,test/hdd/hdd.img,sectorsize=4096,size=20G,split=1G,sparse

So this is how it looks on disk:

$ ls -lah
total 2785264
drwxr-xr-x  23 dark  staff   782B Jan 16 01:27 .
drwxr-xr-x   9 dark  staff   306B Jan 16 01:27 ..
-rw-rw----   1 dark  staff   531M Jan 16 02:50 hdd.img.0000
-rw-rw----   1 dark  staff    12K Jan 16 01:18 hdd.img.0001
-rw-rw----   1 dark  staff   5.9M Jan 16 02:50 hdd.img.0002
-rw-rw----   1 dark  staff    24K Jan 16 01:18 hdd.img.0003
-rw-rw----   1 dark  staff   110M Jan 16 02:48 hdd.img.0004
-rw-rw----   1 dark  staff     0B Jan 16 01:11 hdd.img.0005
-rw-rw----   1 dark  staff   172M Jan 16 02:50 hdd.img.0006
-rw-rw----   1 dark  staff     0B Jan 16 01:11 hdd.img.0007
-rw-rw----   1 dark  staff   207M Jan 16 02:50 hdd.img.0008
-rw-rw----   1 dark  staff     0B Jan 16 01:11 hdd.img.0009
-rw-rw----   1 dark  staff    15M Jan 16 02:48 hdd.img.0010
-rw-rw----   1 dark  staff     0B Jan 16 01:11 hdd.img.0011
-rw-rw----   1 dark  staff    46M Jan 16 01:24 hdd.img.0012
-rw-rw----   1 dark  staff     0B Jan 16 01:11 hdd.img.0013
-rw-rw----   1 dark  staff   151M Jan 16 02:50 hdd.img.0014
-rw-rw----   1 dark  staff    12K Jan 16 01:18 hdd.img.0015
-rw-rw----   1 dark  staff    97M Jan 16 02:50 hdd.img.0016
-rw-rw----   1 dark  staff   5.3M Jan 16 02:48 hdd.img.0017
-rw-rw----   1 dark  staff     0B Jan 16 01:11 hdd.img.0018
-rw-rw----   1 dark  staff   4.0K Jan 16 01:15 hdd.img.0019
-rw-rw----   1 dark  staff    20M Jan 16 02:48 hdd.img.lut

The dump you see here is of an image where I just installed Ubuntu server 15.10.
Instead of wasting 20GB of space this one only needs about 1.3GB. Speed is about the same as before (with a SSD as backing storage) but may suffer severely on a spinning rust disk as there are way more seeks if the sectors become fragmented.

Where to get it

Currently you will have to compile yourself, just fetch the sparse-disk-image branch from https://github.com/dunkelstern/xhyve and execute make.

Installing Ghost via Docker

my Blog is running on Ghost. Ghost is cool but the thing is: most people do not know about node.js or how to setup a node.js application.

But you don't have to!

Virtualization or Containers

You could run a virtual machine with Xen or Virtualbox and just use an appliance that somebody already created for you. But this does not scale when you want to run more than a couple of instances on a server.

So how to set up a server without exactly knowing what to run (and how) but while not using a virtual machine? The answer to that could be Docker.

1. Setup Docker on Ubuntu (14.04+)

This, like all other steps in this guide is straightforward:

$ sudo apt-get install docker.io

Docker is a very lightweight pseudo-virtualization framework building on the foundation of linux cgroups and chroot jails, think of it as some kind of changeroot environment that is even stricter than a normal chroot jail. It restricts the access to all resources not part of the jail. You will see the processes running when you're looking at the process list from the outside of the jail and may even be able to kill them, but from the inside of the container you will not be able to access anything on the outside.

So the overhead of the container running the ghost service will be minimal, it needs some more resources than just running the node server directly (shared libraries have to be loaded twice for example, and a minimal os image will be installed too) but a good server will be able to run quite a couple instances without breaking down.

2. Get the ghost docker image

The next step is downloading the official docker image for the ghost service:

$ sudo docker pull dockerfile/ghost

This will take a while because the ghost docker image is a layered image. Docker creates a differential image for each action that is run while provisioning the container, so you could see what every single command executed did to the container and roll back a few steps if something went wrong or you'd have to update a single component in the history.

If you want to get an overview what exactly happened with an image over time run the history command on it:

$ sudo docker history dockerfile/ghost
IMAGE               CREATED             CREATED BY                                      SIZE
7fd9622ac59b        11 days ago         /bin/sh -c #(nop) EXPOSE map[2368/tcp:{}]       0 B
e052bd394625        11 days ago         /bin/sh -c #(nop) CMD [bash /ghost-start]       0 B
8951c214a253        11 days ago         /bin/sh -c #(nop) WORKDIR /ghost                0 B
083fc6513232        11 days ago         /bin/sh -c #(nop) VOLUME ["/data", "/ghost-ov   0 B
50b7f9b06075        11 days ago         /bin/sh -c #(nop) ENV NODE_ENV=production       0 B
34de0ad45f77        11 days ago         /bin/sh -c #(nop) ADD file:27b2fabfe632ee15b9   880 B
abe6497bce46        11 days ago         /bin/sh -c cd /tmp &&   wget https://ghost.or   71.38 MB
65f8a4200da9        11 days ago         /bin/sh -c #(nop) CMD [bash]                    0 B
5c85a5ac1a37        11 days ago         /bin/sh -c #(nop) WORKDIR /data                 0 B
7a5fa70ca2f3        11 days ago         /bin/sh -c cd /tmp &&   wget http://nodejs.or   17.73 MB
1d73c42b2c8b        12 days ago         /bin/sh -c #(nop) CMD [bash]                    0 B
b80296c7dcea        12 days ago         /bin/sh -c #(nop) WORKDIR /data                 0 B
b90d7c4116a7        12 days ago         /bin/sh -c apt-get update &&   apt-get instal   56.41 MB
036f41962925        12 days ago         /bin/sh -c #(nop) CMD [bash]                    0 B
6ca8ad8beff9        12 days ago         /bin/sh -c #(nop) WORKDIR /root                 0 B
caa6e240bc5e        12 days ago         /bin/sh -c #(nop) ENV HOME=/root                0 B
95d3002f2745        12 days ago         /bin/sh -c #(nop) ADD dir:a0224129e16f61bf5ca   80.57 kB
2cfc7dfeba2d        12 days ago         /bin/sh -c #(nop) ADD file:20736e4136fba11501   532 B
e14a4e231fad        12 days ago         /bin/sh -c #(nop) ADD file:ea96348b2288189f68   1.106 kB
4c325cfdc6d8        12 days ago         /bin/sh -c sed -i 's/# \(.*multiverse$\)/\1/g   221.9 MB
9cbaf023786c        12 days ago         /bin/sh -c #(nop) CMD [/bin/bash]               0 B
03db2b23cf03        12 days ago         /bin/sh -c apt-get update && apt-get dist-upg   0 B
8f321fc43180        12 days ago         /bin/sh -c sed -i 's/^#\s*\(deb.*universe\)$/   1.895 kB
6a459d727ebb        12 days ago         /bin/sh -c rm -rf /var/lib/apt/lists/*          0 B
2dcbbf65536c        12 days ago         /bin/sh -c echo '#!/bin/sh' > /usr/sbin/polic   194.5 kB
97fd97495e49        12 days ago         /bin/sh -c #(nop) ADD file:84c5e0e741a0235ef8   192.6 MB
511136ea3c5a        16 months ago                                                       0 B

As you can see with the official docker image for ghost it builds on a rather old version of ubuntu that is about 16 months old (it's 12.04 LTS, the old version is used currently because most docker images are based on that, so if you run multiple different images you'll only waste those 192.6 MB once as the base layer could be recycled).

3. Setup a user to run ghost from

Of course you could run the ghost docker container from your default user on the system, but I prefer to separate services by user, so I created a new user on the system:

$ sudo adduser ghost

You'll have to put that user into the docker group so it would be able to run docker commands:

$ sudo usermod -G docker ghost

4. Download latest ghost and themes

All things we do from this step on we will run as the new ghost user, so just switch over:

$ sudo su - ghost

Fetch latest ghost release zip to get our hands on the example configuration file and the default casper theme:

$ wget https://ghost.org/zip/ghost-latest.zip
$ mkdir ghost-latest
$ cd ghost-latest
$ unzip ../ghost-latest.zip

Now we copy the important parts to our data directory that the ghost instance will use:

$ cd
$ mkdir mysite.com
$ cd mysite.com
$ cp -r ../ghost-latest/content .
$ cp ../ghost-latest/config.example.js config.js

Now we have a working directory structure and a example configuration file that we can adapt to our preferred settings.

5. Configuring ghost

The simplest thing we could do is just edit the example-config we just copied and add our domain-name to it (config->production->url):

var path = require('path'),
    config;

config = {
    production: {
        url: 'http://mysite.com',
        mail: {},
        database: {
            client: 'sqlite3',
            connection: {
                filename: path.join(__dirname, '/content/data/ghost.db')
            },
            debug: false
        },

        server: {
            host: '0.0.0.0',
            port: '2368'
        }
    }
}

be sure to set the config->production->server->host setting to 0.0.0.0 to be able to access the server later on.

6. Running ghost in docker

We pulled the docker image in step 2, now lets use it:

$ docker run -d -p 2300:2368 -v $HOME/mysite.com:/ghost-override dockerfile/ghost

If everything worked we now can access the ghost instance on http://localhost:2300 or better yet: http://mysite.com:2300

If something went wrong we can inspect the logfile of the ghost instance by running the docker log <id> command. For that we have to find out the <id> part:

$ docker ps
CONTAINER ID        IMAGE                     COMMAND             CREATED             STATUS              PORTS                              NAMES
e425352a4b49        dockerfile/ghost:latest   bash /ghost-start   2 minutes ago        Up 2 minutes         2300/tcp, 0.0.0.0:2300->2368/tcp   mad_galileo

You can use the container ID or the name of the container for all commands that will accept an ID.

$ docker logs -f mad_galileo

If you specify the -f flag, as in the example, the log viewer works like tail -f (follows the log if new entries are appended) if you omit the -f it just dumps what has been logged so far and exits.

7. Setting up a reverse proxy to route multiple domains

Normally, if only one instance runs on the server we could just change the port 2300 in the docker command to 80 and be done. But all the setup we did was to have multiple instances running on the same server and sharing the port 80 for different domains.

As we can not bind more than one docker container to a single port we just have to setup a reverse proxy that listens to port 80 and does the routing to the different ghost instances for us.

I chose varnish for that as it is easy to configure.
For installation of varnish we change back to a user that can use sudo.

7a. Install varnish

Varnish is in the standard ubuntu repositories, so installation is just one apt-get away:

$ sudo apt-get install varnish

The default installation of varnish will listen on a somewhat arcane port to not interfere with apache. As we want varnish to do the routing we re-configure varnish to listen on port 80 and move the apache out of the way.

To do that:

7b. Move apache out of the way

Just change the listening port of apache to some other port not currently in use and make it listen only on 127.0.0.1 as we don't have to access the direct apache port from the outside. You'll find the configuration for that in /etc/apache2/ports.conf:

NameVirtualHost 127.0.0.1:8080
Listen 127.0.0.1:8080

<IfModule mod_ssl.c>
    NameVirtualHost *:443
    Listen 443
</IfModule>

<IfModule mod_gnutls.c>
    NameVirtualHost *:443
    Listen 443
</IfModule>

Also we have to change all the VirtualHost statements in /etc/apache2/sites-available/* to reflect this change:

<VirtualHost 127.0.0.1:8080>

Do not reload the apache config yet as your sites would go offline, but we don't want to interrupt anybody, do we?

7c. Setup varnish to run on port 80

So to move varnish to listen to port 80 instead of 6081 we have to change /etc/default/varnish:

DAEMON_OPTS="-a :80 \
             -T localhost:6082 \
             -f /etc/varnish/default.vcl \
             -S /etc/varnish/secret \
             -s malloc,256m"

7d. Setup routing in varnish to make apache available again

So we don't want to interrupt the connection to the apache daemon to allow for "normal" websites aside of our new ghost instances, to make that possible we set up a default route in /etc/varnish/default.vcl:

backend apache {
    .host = "127.0.0.1";
    .port = "8080";
}

sub vcl_recv {
}

If you now reload the apache config and afterwards the varnish server all sites should be accessible as they were before you made the change:

$ sudo service apache2 restart
$ sudo service varnish restart

If everything is working so far we are ready to add the ghost instances:

7e. Setup routing to ghost instances

As we did for apache, we just add a few rules to /etc/varnish/default.vcl and restart varnish afterwards:

backend ghost_mysite_com {
        .host = "127.0.0.1";
        .port = "2300";
}

sub vcl_recv {
        if (req.http.host ~ "mysite.com") {
                set req.backend = ghost_mysite_com;
                return(pass);
        }
}

If you don't want the varnish server to act as a cache (which it is very good at) you could use return(pipe) to disable that.

Be sure the apache backend is always the first backend defined because that is the default varnish falls back to if no rule in vcl_recv matches and redirects to another backend.

8. Make it permanent

If your server reboots, the currently running docker containers will not be started by default, so we add the command to run them to /etc/rc.local to execute them on reboot automatically:

su ghost -c 'docker run -d -p 2300:2368 -v /home/ghost/mysite.com:/ghost-override dockerfile/ghost'

just append that line before the exit 0 statement at the end.

9. Make it a farm

Now what if you want to run multiple instances?

  • Add a new data directory in /home/ghost (see steps 4 and 5)
  • Run a new docker instance on a different port (step 6 but change the 2300)
  • Add a rule to /etc/varnish/default.vcl for that instance (step 7e, change the 2300 again)
  • Add a line to /etc/rc.local, use the changed command line from step 6 (or change the 2300 again ;) )