To change RAM size, VDISK size or VCPU count of an openstack instance you have to use nova resize. You can't change for e.g. just the RAM size with a parameter, you have to assign a new/other flavor. If there is no suitable flavor for the new properties of the VM, create a new one.

nova resize [--poll] <server> <flavor>

The resize could take a while, after it is finished, the VM boots up with the new specifications. SSH into the VM and check if everything is alright...

Say we want …

• to create a Gallery that has a name and has_many :images, which in turn have a caption
• to offer the user a single form to create a gallery with any number of images
• immediate uploads with a progress bar per image
• a snappy UI

Enter jQuery File Upload. It's a mature library that can do the job frontend-wise. On the server, we'll use Carrierwave, because it's capable of caching images.

(FYI, [here's how to do the u...

You login to a Linux server with a performance issue: what do you check in the first minute?

uptime
dmesg | tail
vmstat 1
mpstat -P ALL 1
pidstat 1
iostat -xz 1
free -m
sar -n DEV 1
sar -n TCP,ETCP 1
top

Also see:

• How to get a rough picture about a Rails project
• How to examine an unknown Ruby object

sslscan is a nice tool to show details about TLS/SSL connections:

~> sslscan some-host-at.makandra.de

Testing SSL server some-host-at.makandra.de on port 443

  Supported Server Cipher(s):
    Failed    SSLv3  256 bits  ECDHE-RSA-AES256-GCM-SHA384
    Failed    SSLv3  256 bits  ECDHE-ECDSA-AES256-GCM-SHA384
    Failed    SSLv3  256 bits  ECDHE-RSA-AES256-SHA384
    Failed    SSLv3  256 bits  ECDHE-ECDSA-AES256-SHA384
    Rejected  SSLv3  256 bits  ECDHE-RSA-AES256-SHA
...

  Prefered Server Cipher(s):
    TLSv1  128 bits  ECDHE-RSA-A...

This describes all the steps you'll need to get Solr up and running for your project using the Sunspot gem.

Prepare Sunspot on your development machine

What you want in your Gemfile:

gem 'sunspot_rails'
gem 'sunspot_solr'
gem 'progress_bar' # for sunspot:solr:reindex

Now define what should be indexed within Solr from your ActiveRecord models, e.g.,

class Article << ActiveRecord::Base

  searchable do
    text :title
 ...

In case you want to require a gem, that is not in the Gemfile of you bundle and therefore not in your loadpath, you need to add the path manually and require the gem afterwards.

Expected error

Requiring a gem, that is not in the Gemfile or .gemspec, will cause an LoadError exception:

require 'example_gem' => LoadError: cannot load such file -- example_gem

Adding a gem to the loadpath temporary

1. You need to install the gem

gem install 'example_gem'

2. Then you need to require the path where the gem was install...

Website that offers lots of different kinds of HTTPS configurations, bad or good or complicated.

They also offer a dashboard to check if your browser's HTTPS handling works as expected (which might be compromised e.g. due to security products or enterprise proxy servers).

Changes:

• Geordi is now (partially) tested with Cucumber. Yay!
• geordi cucumber supports a new @solo tag. Scenarios tagged with @solo will be excluded from parallel runs, and run sequentially in a second run
• Support for Capistrano 2 AND 3 (will deploy without :migrations on Capistrano 3)
• Now requires a .firefox-version file to set up a test firefox. By default now uses the system Firefox/a test Chrome/whatever and doesn't print warnings any more.
• geordi deploy --no-migrations (aliased -M): Deploy with `cap ...

When deploying with capistrano it's possible you get this "error" message:

*** [err :: example.com] There are no Phusion Passenger-served applications running whose paths begin with '/var/www/example.com'.
*** [err :: example.com] 

This is just because there were no running passenger process for this application on the server which could be restarted. It's not a real error. The application process will start if the first request for this app hits the appserver.

The output appears as err because it's printed to stderr.

Dep...

The attached article outlines considerations when choosing client-side vs. server-side implementations of the Google Geocoding APIs (geocoder, directions, not maps drawing). The main points are:

• On the server side you only get a fixed daily request quota
• On the client side the quota is per-client, so basically unlimited
• When implementing APIs on the server-side, be aware that quota is measured by IP. When hosting in the cloud **you don't always know which other services might...

Rails has the handy controller method send_file which lets us download files easily. We can decide whether the file should be downloaded (disposition: 'attachment') or shown in the browser (disposition: 'inline'). The default is disposition: 'attachment'.

Downloading files will not work when you are calling the controller action from an AJAX request. The browser will try to render the file and insert it in the DOM, which is never what you want.

Unpoly 2

Unpoly (sin...

You are getting when connecting via SSH or deploying with Capistrano (which uses SSH):

Too many authentication failures for username

This is caused by having too many SSH keys added to your keyring or ssh-agent. Your ssh-agent will throw all keys against a server until one matches. Most servers will deny access after 5 attempts.

This issue might come and go as the order of the active SSH keys in your ssh-agent changes.

Quick fix

Have less keys. Up to 5 keys are fine when the SSHD you're connecting to is using the default ...

• Improve geordi cucumber: Only attempt @solo run when the specified files contain the @solo tag, skip @solo run if any filename is passed with a line number (e.g. features/example.feature:3)
• Improve geordi deploy: Find stages by their prefix (e.g. s -> staging, m -> makandra), bundle if needed, check the selected stage exists
• Improve geordi server: Takes port as argument (e.g. geordi ser 3001), option --public (-P) starts the server with -b 0.0.0.0 to make it accessible from other machines in the local network, e.g. ...

I had trouble serving an MP4 video to my iPad. Although the video complied with all the specs (H.264 codec, up to 1080p, 30 FPS) I always got this error:

This video could not be loaded, either because the server or network failed or because the format is not supported: http://10.40.0.177:3000/video.mp4

After spending a lot of time fighting this issue, I tried to upload the same unchanged video file to a production server (Apache / Passenger). It worked immediately. I guess iOS is picky about some HTTP header that my local HTTP server (Th...

In case https://www.rubydoc.info/ is to slow or offline, you can also read a gem documentation offline.

Start a server with gem server and go to http://0.0.0.0:8808/. Here you will find a list of all installed gems and it is possible to navigate to the documentation if installed e.g. http://0.0.0.0:8808/doc_root/rubocop-0.77.0/

In case you set the configured RubyGems to not install documentation by default, you need to add generate the documentation for the specific gem.

gem install rubocop --document
`...

Was ist Elastic?

• Suchmaschine, basierend auf Apache Lucene
• größtenteils Open-Source
• einige kommerzielle Features ("Elastic Stack", früher "X-Pack")
  • Zugriffsrechte (bis vor kurzen)
  • Monitoring
  • Reporting
  • Graph-Unterstützung
  • Machine Learning
• REST-Api (JSON über HTTP)

Grundlagen

Elastic antwortet per Default auf Port 9200

http GET :9200

{
  "name": "ntK2ZrY",
  "cluster_name": "elasticsearch",
  "cluster_uuid": "Bbc-ix5bQZij5vfFU29-Cw",
  "version": {
    "number": "6.7.1",
    "build_flavor": "...

Starting from Rails 4.0, you can use a special form options helper called #collection_check_boxes. It behaves similar to #collection_select, but instead of a single select field it renders a checkbox and a label for each item in the collection.

= form_for @post do |form|
  = form.collection_check_boxes :author_ids, Author.all, :id, :name_with_initial

How generated form params look like
---------------------------------...

In my case [...] the catalog is an XML that contains all kinds of possible products, categories and vendors and it is updated once a month. When you read this file with the Nokogiri default (DOM) parser, it creates a tree structure with all branches and leaves. It allows you to easily navigate through it via css/xpath selectors.

The only problem is that if you read the whole file into memory, it takes a significant amount of RAM. It is really ineffective to pay for a server if you need this RAM once a month. Since I don't need to n...

When you need to patch an existing gem, one way is to "vendor" the gem by copying it into the vendor/gems directory of your Rails project. You can then make any changes you require and Rails will use the vendored version of the gem after a server restart. Unfortunately you need to perform some additional steps to marry Rails and the copied gem. This notes describes what to do.

With Bundler

This is super-painful. If you just copy the gem to vendor/gems, Rails will complain:

Unpacked gem foolib in vendor/gems has no s...

Capistrano automatically logs each (successful) deployment into a file on your application servers.

It is located at the root of your server's project folder, i.e. the parent of releases and current, like so:

/var/www/your-project$ ls
current
log
releases
repo
revisions.log  <---  here
shared

Each line in that file contains the deployed branch, commit, release ID, and username (was read from the deploying user's machine):

$ tail -n3 revisions.log 
Branch master (at da45511bea63002ac2ff002d1692e09d0dd7cb88) deployed as rel...

When you simply want to get to know Puppet, follow puppetlabs’ Learning Puppet Docs. They give you a handy introduction inside a virtual machine they provide. You can watch the talk by Garrett Honeycutt 'Expanded Introduction to Puppet'.

Do not miss their cheatsheat and their [learn-puppet virtual machine](http://info.puppetl...

By default Middleman generates files with a .html extension. Because of this all your URLs end in /foo.html instead of /foo, which looks a bit old school.

To get prettier URLs, Middleman lets you activate :directory_indexes in config.rb. This makes a directory for each of your pages and puts a single file index.html into it, e.g. /foo/index.html. This lets you access pages with http://domain/foo.

Don't double your requests!

Unfortunately you are now forcing every br...

In order to request a SSL certificate from any dealer, you usually need a CSR certificate. As both the CSR as well as key are created in this step, make sure you save this certificate on a trusted, secure machine only. Usually this is your production environment.

Run this on the server (not on your machine) as root.\
Replace your-domain.tld with the domain you request the certificate for and YYYY with the current year so you will not have any conflicts when requesting a certificate next year.

openssl req -new -sha256 -out www.your-dom...

You want to test your 1GE or 10GE internet uplink? We needed to ensure we have full 10GE to the backbone for a customer project.

Using netcat

To test whether we can achieve the bandwidth internally, you can use netcat and dd like this:

On your first server: nc -v -l 55333 > /dev/null
On your second server: dd if=/dev/zero bs=1024K count=5000 | nc -v $remote_ip 55333

You should see some output like this:

user@xxx:~ % dd if=/dev/zero bs=1024K count=5000 | nc -v removed 55333
Connection to 91.250.95.249 55333 port [...