Jul 092016

Since moving Docker containers is easy, and Amazon keeps on patching and rebooting my little AWS server, time to put the theory into practice and move to some other place.

Moving was 4 parts:

  • Copy the data volumes over
  • Change DNS
  • Configure the load balancer
  • Start everything in the new place

The first one needed some scripting since moving data containers in Docker is not a built-in function. And that needs a corresponding restore function of course. Here the scripts, first backup:

# Does a backup from one or many Docker volumes
# Harald Kubota 2016-07-09

if [[ $# -eq 0 ]] ; then
 echo "Usage: $0 docker_volume_1 [docker_volume_2 ...]"
 echo "will create tar.bz2 files of the docker volumes listed"
 exit 10

today=`date +%Y-%m-%d`

for vol in "$@" ; do

 echo "Backup up docker volume $i into $backup_file"
 docker run --rm -v $vol:/voldata -v $(pwd):/backup debian:8 \
 tar cf /backup/$vol.tar.tmp /voldata
 bzip2 <$vol.tar.tmp >$backup_file && rm -f $vol.tar.tmp

and here restore:

# Restore a tar dump back into a Docker data volume
# tar file can be .tar or .tar.bz2
# Name is always VOLUME-NAME-20YY-MM-DD.tar[.bz2]
# Harald Kubota 2016-07-09

if [[ $# -ne 1 ]] ; then
 echo "Usage: $0 tarfile"
 echo "will create a new volume derived from the tarfile name and restore the tarfile data into it"
 exit 10

today=`date +%Y-%m-%d`

for i in "$@" ; do

 volumename=$(echo $i | sed 's/\(.*\)-20[0-9][0-9]-[0-9][0-9]-[0-9][0-9]\.tar.*/\1/')
 docker volume create --name $volumename

 # if .bz2 then decompress first

 echo "Restoring tar file $i into volume $volumename"

 if [[ ${last4} == ".bz2" ]] ; then
 tar_name=$(basename $i .bz2)
 bunzip2 <$i >$tar_name
 #echo "tar_name=$tar_name, delete_tar=$delete_tar"

 docker run --rm -v $volumename:/voldata -v $(pwd):/backup debian:8 \
 tar xfv /backup/$tar_name
 if [[ $delete_tar -eq 1 ]] ; then
 rm $tar_name

With this, moving Docker volumes is a piece of cake, and it doubles as a universal backup mechanism too.

Updating DNS is trivial, as is the Load Balancer part which maps the popular port 80 to the correct Docker instance. Starting is a simple “docker-compose up”.

Mar 062016
Using HAProxy with Web Mirrors

Setting up dockerized webmirrors is easy with this

docker run -e web_source="http://www.theregister.co.uk/" -e port=3402 --expose=3402 -P --name=mirror_theregister -d hkubota/webmirror

and you’ll get a descent copy of The Register’s web page on port 3402. Thus access is via http://this.host:3402

Accessing would be nicer via a virtual hostname (e.g. theregister-mirror.this.host). That’s where HAProxy comes into play: as a reverse proxy. I found the basics here.

Here the complete start script:

# Create a valid and usable configport_blog=`docker inspect mirror_haraldblog | jq -r '.[0].NetworkSettings.Ports."3401/tcp"[0].HostPort'`
port_reg=`docker inspect mirror_theregister | jq -r '.[0].NetworkSettings.Ports."3402/tcp"[0].HostPort'`

cat <~/haproxy/config/haproxy/haproxy.cfg
 user haproxy
 group users
 # Admin socket 
 stats socket /var/run/haproxy.sock mode 600 level admin 
 stats timeout 2m

 # Default SSL material locations
 #ca-base /etc/ssl/certs
 #crt-base /etc/ssl/private

# Default ciphers to use on SSL-enabled listening sockets.
# For more information, see ciphers(1SSL).
#ssl-default-bind-ciphers kEECDH+aRSA+AES:kRSA+AES:+AES256:RC4-SHA:!kEDH:!LOW:!EXP:!MD5:!aNULL:!eNULL

 log global
 mode http
 option httplog
 option dontlognull
 timeout connect 5000
 timeout client 50000
 timeout server 50000
 errorfile 400 /etc/haproxy/errors/400.http
 errorfile 403 /etc/haproxy/errors/403.http
 errorfile 408 /etc/haproxy/errors/408.http
 errorfile 500 /etc/haproxy/errors/500.http
 errorfile 502 /etc/haproxy/errors/502.http
 errorfile 503 /etc/haproxy/errors/503.http
 errorfile 504 /etc/haproxy/errors/504.http
 stats enable 
 stats uri /stats 
 stats realm Haproxy\ Statistics 
 stats auth admin:ADMIN_PASSWORD
frontend http-in
 bind *:80
 acl is_site1 hdr_end(host) -i www1.studiokubota.com
 acl is_site2 hdr_end(host) -i www2.studiokubota.com
 use_backend site1 if is_site1
 use_backend site2 if is_site2

backend site1
 balance first
 option httpclose
 option forwardfor
 server realblog harald.studiokubota.com:80 maxconn 32 check
 server mirrorblog studiokubota.com:${port_reg} maxconn 32 check
 stats admin if true
backend site2
 balance roundrobin
 option httpclose
 option forwardfor
 server s2 studiokubota.com:${port_blog} maxconn 32

listen admin
 bind *:1936
 stats enable
 stats admin if TRUE

docker run -v ~/haproxy/config:/config -p 80:80 -d -p 1936:1936 hkubota/haproxy

Via HAProxy you can access the mirrors via http://www1.studiokubota.com resp. another mirror at http://www2.studiokubota.com, which are much nicer to use.

This setup is probably something for docker-compose if this was one application.

Update 2016-05-03: Enable admin interface: disable/enable backend servers via http://host:1936/haproxy?stats


Jan 242016
AWS does not like my Docker :-(

My WordPress/MySQL Docker instances on AWS are unhappy: after some time, they stop. No idea why. All I see is

Failed Units: 1

when I log in after WordPress seems to have died. And no Docker process is running. While I can restart them easily, it’s annoying to do so manually. At this point I have 2 possibilities: find the root cause, or work around it via monitoring and automatic restarting when needed.

And a load balancer to make the service available even when AWS does kill my Docker containers would be nice. Actually a load balancer has to do monitoring anyway. Since this topic came up at work too, it’s double useful. So a load balancer it is!

A nice article, although a bit dated, is here. He knows what he’s talking about: he made up elastic binary trees and wrote haproxy and made it saturate a 10G link back in 2009.

nginx is a popular http load balancer (amond other things it can do), but since haproxy can do TCP in general, it’s more universally suitable for me, so that’s what it’ll be.

Step 1 is to have something to load balance. Because this is blog runs on WordPress with its MySQL instance, doubling this is non-trivial: WordPress keeps files in its web directory, and the MySQL instanced would need a multi-master replication setup.

Instead I’ll have a static copy of the web page…and then use a load balancer to switch to the static page when the primary is dead.

PS: To be fair AWS might not be at fault here. Truth is: I don’t know what’s causing the problem. On Google Cloud I had no such issue, but that’s about all I can say. I don’t expect problems in the Docker containers as they are quite literally identical. Even the version of CoreOS is identical.

Anyway, this all sounds like a good excuse to set up some load balancing and monitoring.


Jan 092016

Docker has a PID 1 problem: On normal Unix systems his is the init process which does 3 important things (and some more):

  1. Adopt orphans
  2. Reap zombies
  3. Forward signals

There are 2 ways to start processes in a Docker container:

  1. CMD <command> <param1> <param2>…
  2. CMD [“executable”, “param1”, “param2”,…]

In the first case a shell (/bin/sh) runs your program, so PID 1 is /bin/sh. In the 2nd case your executable gets PID 1. Neither is good as neither can do what init normally does.

A fix is to run a proper init system (systemd, SysV init etc.) but that’s way more than you need. A more appropriate fix is to use a simple or dumb init. Like this: https://github.com/Yelp/dumb-init

A nice write-up from the Yelp engineering blog: http://engineeringblog.yelp.com/2016/01/dumb-init-an-init-for-docker.html

Note that this is not needed if

  • Your process runs as PID 1 and does not spawn new processes or
  • Your containers live short so that the volume of potential zombie processes won’t matter and
  • you don’t write any data so a sudden SIGTERM from Docker won’t cause issues with data consistency
Jan 022016
Docker Backup

I changed slightly the way to start my containers. Now they always contain the backup volume too:

docker run --name blog-mysql -v blog-backup:/backup \
-v blog-mysql-data:/var/lib/mysql -d mysql/mysql-server:5.7
docker run --name blog-app -v blog-backup:/backup \
--link blog-mysql:mysql -v wordpress-data:/var/www/html -p 80:80 \
-w /var/www/html/wordpress -d wordpress:latest

The reason is that I can run a backup job inside the container. Important for the DB backup as now I can use msqldump. Before it was: stop mysql, tar up the DB files, start MySQL again.

Making a backup in each container:

tar -C /var/www/html -z -f /backup/blog-wp-`data +%Y-%m-%d.tar.gz .


mysqldump -pROOTMYSQLASSWORD --all-databases | gzip >/backup/blog-db-`date +%Y-%m-%d`.tar.gz

Now the problem is how to get those files out and to where…

Dropbox/Google Cloud don’t offer access via ftp/scp/etc. Time to look into the various storage offerings from Google/Amazon/Azure.

Jan 022016
Moving dockerized WordPress

One advantage of Docker is the easy move to other Docker providers. In my case: Moving from Google Cloud to Amazon’s AWS. Same instance size, same OS (CoreOS 877). The main difference is the location: Google’s one is in TW, AWS’s one is in JP.

So I start with my MySQL/Wordpress instance from here to AWS.

  1. Create a t1.micro instance with CoreOS 877 (1 shared CPU, 0.6 GB RAM)
  2. Set up ssh authentication for the main user (core for CoreOS, root usually)
  3. Create 3 docker containers and populate them with the last backup of the current instance of MySQL/Wordpress.
    1. Stop WordPress/MySQL. Mount the data volumes to the backup volume. Run a backup.
    2. Start MySQL/WordPress again
  4. Copy those 2 tar files to the new CoreOS AWS server.
  5. Restore the data volumes.
  6. Here wish that Docker would allow copying data volumes from A to B.
  7. Run the very same docker commands to run MySQL and WordPress.
  8. Change DNS (or test by faking a DNS change on the desktop client which runs the browser)

And lo-and-behold, it worked as expected. No issue at all.

When you can read this, then this blog already moved to run on AWS. I’ll keep it here for a while.

Dec 272015
Wordpress in a Docker

When you read this, this blog moved do a (currently) Google Cloud VM Instance using Docker.

There’s a lot of examples how to set up containers for this combination of WordPress and MySQL, but the migration from an existing installation was nowhere mentioned. Thus here my notes from the end to the start:

Run this blog in Docker

  1. To start I need
    1. a server which can run Docker
    2. Docker 1.9.x as I need the volume command
    3. a MySQL dump of the cold copied DB files: mysql-backup.dump
    4. a tar archive from the wordpress directory: wordpress-backup.tar.gz
    5. a DNS entry to point to the Docker host
    6. Port 80 on the Docker host exposed to a public IP
  2. On the Docker host, create 3 empty data volumes which will host the persistent DB data, wordpress directory and backups:
    docker volume create --name blog-mysql-data
    docker volume create --name wordpress-data
    docker volume create --name blog-backup
  3. Populate blog-backup with the backup files:
    docker run -it -v blog-backup:/backup -v /home/harald:/data debian:8 bash
    cp /data/mysql-backup.dump /data/wordpress-backup.tar.gz /backup
  4. blog-backup is a volume which contains backups in /backup of the wordpress directory as well as the (cold) mysql DB. Extract like this:
    docker run -it -v blog-backup:/backup \
    -v blog-mysql-data:/var/lib/mysql \
    -v wordpress-data:/var/www/html debian:8 bash
    cd /var/lib
    tar xfv /backup/mysql-backup.dump
    cd /var/www/html
    tar xfv /backup/wordpress-backup.tar.gz
  5. Start MySQL Docker container first
    docker run --name blog-mysql \
    -v blog-mysql-data:/var/lib/mysql \
    -d \
  6. Now start WordPress (and replace the passwords and account of course)
    docker run --name blog-app \
    --link blog-mysql:mysql \
    -v wordpress-data:/var/www/html \
    -p 80:80 \
    -w /var/www/html/wordpress \
    -d \

Google Cloud Configuration

When creating the VM which runs Docker, make sure you get Docker 1.9 or newer as the docker volume command does not exist until then. For now (December 2015) that means to choose the beta CoreOS instance for your Google Cloud VM.

Be able to copy files to the VM.

Beside this, make http and https traffic externally visible and remember the IP assigned to the VM.


My DNS is on linode.com, so I have to change the blog DNS entry there. TTL is now 5min (instead of 1h default) to make testing a bit faster.

Alternative during testing it’s sufficient to make the machine which runs the browser to point the FQDN to the current IP. The Docker host or container does not care about its external IP.

Initial Polulation of the DB Filesystem

The first population of the MySQL data was a bit tedious and manual due to the unexpected upgrade needed.

  1. Have a dump from the SQL DB:
     mysqldump -pMY_ADMINPW --all-databases > mysql-backup.dump
  2. Run mysql with the dump being available. Mount the directory which has the dump in /data2 and the (empty) blog-mysql-data under /var/lib/mysql and set an initial DB root password:
    docker run -it \
    -v /home/harald/dockerstuff/mysql-data:/data2 \
    -v blog-mysql-data:/var/lib/mysql \
    -e MYSQL_ROOT_PASSWORD=mypw -P mysql/mysql-server:5.7
  3. Since we did not name this container, we have to find its name or container ID:
    CONTAINERID=`docker ps --format "{{.ID}} {{.Image}}" | grep mysql-server | awk '{print $1}'`
    docker exec -it $CONTAINERID bash
  4. Inside the mysql container now run the import:
    mysql -u root -pmypw </data2/mysql-backup.dump
  5. and do a DB upgrade and stop mysql:
    mysql_upgrade -u root -p mypw
    pkill -SIGTERM mysqld
  6. By now the DB root password is change to the one from the dump. And blog-mysql-data now has a working MySQL DB with the last dump we took.


Initial Population of the WordPress Filesystem

I tried initially to use a plan vanilla WordPress Docker as unmodified as possible, but since I needed to add plugins and themes, I tried to find a programmatic way to add them. While thinking about future updates of WordPress and its plugins, it made me realize that a separate data volume for the wordpress directory is in order. The alternative would have been to rewriting /entrypoint.sh in the original WordPress Docker container.

  1. Start the WordPress Docker container with no modifications but let it connect to the MySQL container:
    docker volume create --name wordpress-data
    docker run -it --name blog-app \
    --link blog-mysql:mysql \
    -v wordpress-data:/var/www/html \
    -p 80:80 \
    -w /var/www/html/wordpress wordpress:latest
  2. The /entrypoint.sh script will populate /var/www/html/ with a complete WordPress instance. Changing the WORKDIR to /var/www/html/wordpress puts those files to where I need them as that’s where the files are on the old server.
  3. Now you can stop the WordPress container. The data files are kept.
  4. I had to put a lot of my uploaded images back:
    docker run -it -v /home/harald:/data2 \
    -v wordpress-data:/var/www/html debian:8 bash
  5. Inside the Debian container copy the files to wordpress/wp-content/uploads
    cp -pr /data2/wordpress/wp-content/uploads/* /var/www/html/wordpress/wp-content/uploads/
  6. MySQL container was running at this time. Starting the WordPress container now again:
    docker run -it --name blog-app \
    --link blog-mysql:mysql \
    -v wordpress-data:/var/www/html \
    -p 80:80 \
    -w /var/www/html/wordpress wordpress:latest
  7. For testing, edit /etc/hosts of the machine with the browser to make the FQDN of the blog point to the IP of the Docker host.
  8. Now in a browser I was able to see everything from my blog, log in, update Askismet, install YAPB and install the theme Suffusion.
  9. Stop the container, mount the data volume as before, and create a tar dump of /var/www/html/wordpress as wordpress-backup.tar.gz
    docker stop blog-app
    docker run -it -v wordpress-data:/var/www/html \
    -v /home/harald:/data2 debian:8 bash
    cd /var/www/html
    tar cfvz /data2/wordpress-backup.tar.gz wordpress

At this point wordpress-data is the complete wordpress directory and I have a tar archive of it.

Outstanding Items



MySQL is easy enough manually:

docker exec -it blog-mysql bash

Inside run a mysqldump. Then transfer the dump to a place off-site. Automate by not using bash but instead call the script to make the backup. Or run mysqldump from another server but i think that causes more network traffic. I’d need to expose the mysql ports for the latter though.


WordPress directory is equally easy:

docker exec -it blog-app bash

Inside again run a tar and/or rsync to a remote site.

Potential Issues

  • MySQL and WordPress currently must run on the same Docker host. To have them on separate hosts a network needs to be created to connect those.
    However I would have been ok to have MySQL and WordPress in one container as I plan not to scale. Right now I use the micro-instance of Google Cloud and I’m fine with this.
  • Disk space on the Docker host. It’s limited. 10G Google gives me (resp. I assigned myself).
    volumes use all disk space they can get, so the backup volume WILL increase if I do dayly dumps inside with no expiration. I plan to move them off-size though, so I can delete old backups quickly.
  • If the Docker hosts fails/restarts, I have to manually restart my 2 containers.
  • CPU/RAM of the f1-micro instance (1 shared CPU, 0.6GB RAM): it’s enough, but memory is used up:
    total       used       free     shared    buffers     cached 
    Mem:        607700     580788      26912      33404      12284     122960 
    -/+ buffers/cache:     445544     162156 
    Swap:            0          0          0


  • Note that the debian:8 image contains neither bzip2 nor xz.
Dec 062015
Google Cloud and Docker

Using the developer console of Google Cloud, deploying a CoreOS VM, connecting to it, using docker commands to start a Docker container was easy.

Here now the console version:

# Might need this once:
ssh-agent bash
ssh-add google_compute_engine
gcloud components update
gcloud config set compute/zone asia-east1-b
# Start instance
gcloud compute instances start instance-1
# See what we got
gcloud compute instances describe instance-1
# Set DNS
gcloud dns record-sets transaction start --zone="kubota7"
gcloud dns record-sets transaction add --zone="kubota7" --name="mq.kubota7.info." --ttl=300 --type=A ""
gcloud dns record-sets transaction execute --zone="kubota7"
# Add firewall ports to open (port 1883)
gcloud compute firewall-rules create "mqtt" --allow tcp:1883 --description "MQTT traffic" --network "default" --source-ranges ""

Now the fun part! We have an DNS record of a host which can run docker images. We allowed tcp:1883. Now let’s start it:

gcloud compute ssh instance-1 --command "docker run -d -p 1883:1883 hkubota/mosquitto:1.4.5"

Now tearing it all down:

gcloud compute ssh instance-1 --command "docker stop 3f262028d7abd0b9a5efa3b6bfc69c04e378244d8878f5fdf6e81c2ec38b8631"
yes | gcloud compute firewall-rules delete "mqtt"  
gcloud dns record-sets transaction start --zone="kubota7"
gcloud dns record-sets transaction remove --zone="kubota7" --name="mq.kubota7.info." --ttl 300 --type A ""
gcloud dns record-sets transaction execute --zone="kubota7"
gcloud compute instances stop instance-1
Dec 052015
Docker! Docker! Docker!

Played a bit with Docker. I read about it (hard to miss, isn’t it?) and wanted to test this out a bit. Setting up a Docker container, deploy in a cloud and see what you can do.

Turns out: this is not only easy, but it’s very quickly understandable why it’s great for dev-ops style work. And why it’s security-wise difficult to use when dev and ops are separate for regulatory reasons.

Important discoveries and notes:

  • You need an underlying OS to run docker containers. Anything will do as long as it’s Linux with support for needed features:
    • kernel 3.10 or newer
    • aufs
    • cgroups
  • A good choice is CoreOS. Tested, and worked. Very small too. Ubuntu is fine too. As is CentOS. Anything modern really. The only thing this OS does is start/stop docker containers. Plus monitoring them if you want to. And store their images.
  • Your app runs all alone in that container. Thus you can use root, but to protect you from yourself, running as a normal user is preferred. In the Dockerfile that will do it:
USER harald
WORKDIR /home/harald
ENTRYPOINT ["/bin/bash"]


  • Sharing local filesystems or having local data volumes in containers is easy:
# Create a volume and mountpoint src
docker create -v /src --name src debian:8 /bin/true
# View what you did
docker volume ls
# Use via
docker run -it --volumes-from src --user root hkubota/debian-dev:1

  • If you want to have non-local and persistent modifyable filesystems, you are out of luck. Unsolved problem. NFS is one possibility with known drawbacks.
  • If you build a image, it has layers and the build is automate-able and reproducible. If you cannot, then a commit of a running container creates an image too.
  • https://imagelayers.io/ shows nicely how images are built with all those layers.
  • Development creates a lot of images. Many temporary, but they are kept anyway. Use this to clean them up and run via cron (original found here):
docker rm -v $(docker ps -a -q -f status=exited)
docker rmi $(docker images -f "dangling=true" -q)
docker run -v /var/run/docker.sock:/var/run/docker.sock \
-v /var/lib/docker:/var/lib/docker --rm martin/docker-cleanup-volumes
  • Since your container only runs your stuff, it does not run things like cron out of the box. Or any other daemon for that matter. If you need it, have it be part of the container and make sure crond (in this case) starts as part of your container start.
  • If you use e.g. Debian 8 as the main Docker container OS, have a development system to create binaries with and for it. Using Alpine Linux as OS and using pre-compiled binaries won’t work if glibc is expected and non-existant. A re-compile on Alpine will of course solve this.
    So stick to one container OS.
  • Security is a problem if you usually don’t allow people to be root. If you log in on the container host as, becoming root on it is trivial.


  • How to run a DB? It needs persistent storage. How to do replication? How do I do backup?
  • MQTT similar needs persistent storage. A small data volume container will do.
  • Networking. While exposing a port is easy, I did not yet need interconnections between containers.