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  1. Automatically pull updated Docker images and restart containers with docker-puller

    If you use docker.io (or any similar service) to build your Docker containers, it may be possible that, once the new image is generated, you want your Docker host to automatically pull it and restart the container.

    Docker.io gives you the possibility to set a web hook after a successful build. Basically it does a POST on a defined URL and send some informations in JSON format.

    docker-puller listens to these web hooks and can be configured to run a particular script, given a specific hook. It's a very simple service I wrote using Python/Flask. It's also my first Flask application, so if you want to improve it, feel free to send me a pull request on GitHub.

    Note: this is not the only existing service that is able to do this task. I took inspiration from this article http://nathanleclaire.com/blog/2014/08/17/automagical-deploys-from-docker-hub/ and I really tried to customize https://github.com/cpuguy83/dockerhub-webhook-listener for my own needs, but the problem is that dockerhub-webhook-listener is not ready to be used as is (you have to customize it) and I'm not very good with Golang (yet) to be able to do it in little time. This is why I rewrote the service in Python (that is my daily language). I want to thank Brian Goff for the idea and all the people in #docker @ FreeNode for the support.

    How to use docker-puller

    Setting up the service should be quite easy. After you clone the repository from https://github.com/glowdigitalmedia/docker-puller there is a config.json file where you define the host, port, a token and a list of hooks you want to react to. For example:

    {
        "host": "localhost",
        "port": 8000,
        "token": "abc123",
        "hooks": {
            "hello": "scripts/hello.sh"
        }
    }
    

    Create a bash script (in this case it was called hello.sh) and put it under script folder and write the instructions to be executed to pull the new image and restart the container (example):

    docker pull andreagrandi/test:latest
    docker stop test
    docker rm test
    docker run --name test -d -p 8000:80 andreagrandi/test:latest
    

    Once configured, I suggest you to setup a Nginx entry (instructions not covered here) that for example redirect yourhost.com/dockerpuller to localhost:8000 (I would advise to enable SSL too, or people could be able to sniff your token). The service can be started with: "python app.py" (or you can setup a Supervisor script).

    At this point docker-puller is up and running. Go to docker.io automatic build settings and setup a webhook like this: http://yourhost.com/dockerpuller?token=abc123&hook=hello

    Every time docker.io finishes building and pushing your image to the docker registry, it will POST on that URL. docker-puller will catch the POST, check for a valid token, get the hook name and will execute the relative script.

    That's all! I hope this very simple service can be useful to other people and once again, if you want to improve it, I will be glad to accept your pull requests on GitHub.

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  2. How to configure Edimax EW-7811UN Wifi dongle on Raspbian

    If you want to connect your RaspberryPi to your home network and you want to avoid cables, I suggest you to use the Edimax wifi adapter. This device is quite cheap (around £8 on Amazon) and it's very easy to configure on Raspbian (I assume you are using a recent version of Raspbian. I'm using the one released on 20/06/2014).

    edimax-pi3

    Configure the wifi adapter

    Edit /etc/network/interfaces and insert these configuration values:

    auto lo
    iface lo inet loopback
    iface eth0 inet dhcp
    
    allow-hotplug wlan0
    auto wlan0
    
    iface wlan0 inet dhcp
    wpa-ssid YOURESSID
    wpa-psk YOURWPAPASSWORD
    

    Power management issue

    There is a known "issue" with this adapter default configuration that makes it to turn off if the wlan interface is not in use for some minutes. To avoid this you have to customize the parameters used to load the kernel module. First check that your adapter is using 8192cu module:

    sudo lsmod | grep 8192
    8192cu 551136 0
    

    Create the file /etc/modprobe.d/8192cu.conf and insert the following lines inside:

    # prevent power down of wireless when idle
    options 8192cu rtw_power_mgnt=0 rtw_enusbss=0
    

    I also suggest to create a little entry in crontab to make the RaspberryPi ping your router every minute. This will ensure that your wifi connection will stay alive. To edit crontab just type (from pi user, you don't need to be root):

    crontab -e
    

    and insert this line at the end:

    */1 * * * * ping -c 1 192.168.0.1
    

    where 192.168.0.1 is the IP of your router (of course substitute this value with the ip of your router).

    Keep Alive Script

    I created a further script to keep my WIFI alive. This script will ping the router (change the IP using the one of your router) every 5 minutes and if the ping fails it brings down the wlan0 interface, the kernel module for the wifi and bring them up again.

    Just put this script in /root/wifi_recover.sh and then execute from root user:

    chmod +x wifi_recover.sh
    crontab -e
    

    Insert this line inside the crontab editor:

    */5 * * * * /root/wifi_recover.sh
    

    Conclusion

    The configuration is done. Just reboot your RaspberryPi and enjoy your wifi connection.

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  3. Configuring ddclient to update your dynamic DNS at noip.com

    noip.com is one of the few dynamic DNS free services that are reliable to use. If you have, like in my situation, a RaspberryPi connected to your home DSL and you want it to be always reachable without knowing the current IP address (the IP could change if you have a normal DSL service at home), you need a dynamic DNS service.

    To update the noip.com one you just need ddclient a tool that is available in Raspbian/Debian repository. You can install it with this command:

    sudo apt-get install ddclient
    

    then you just need to edit /etc/ddclient.conf

    protocol=dyndns2
    use=web, web=checkip.dyndns.com/, web-skip='IP Address'
    server=dynupdate.no-ip.com
    login=yourusername
    password=yourpassword
    yourhostname.no-ip.org
    

    and restart the client:

    sudo /etc/init.d/ddclient restart
    

    That's all! Please remember that noip.com free accounts have a limitation: they need to be confirmed every 30 days (you will receive an email and you need to click on the link contained to update your DNS).

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