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Management Chef at the same time and get in each other’s way. Role-Out To group multiple cookbooks in a role, create a new file below Roles in the repository, say, beispiel.rb, with the following content: name "beispiel" description "Example of a role" run_list("recipe[emacs]", U "recipe[zsh]", "recipe[git]") This groups the emacs, zsh and git recipes under the beispiel role name. Then send the role to the server like this: Figure 2: The web front end login page: the default password specified on the right is incorrect. Changing the slightly cryptic default after logging in the first time is a good idea. Now go to the Nodes menu. When you get there, click the client name, change to the Edit tab, and finally drag the recipe you want to use from Available Recipes and drop it into the Run List (the recipe will slot into the top position in the list). In the example, you would now see emacs at the top [Figure 3]. To store this assignment, press the Save Node button bottom left on the page. Client-side now, manually launch the chef-client tool: sudo chef‐client This command line immediately opens a server connection, picks up the recipes assigned to the client (only emacs for the time being) and executes the recipes [Figure 5]. To allow this to happen on a regular basis, you should run the client at regular intervals as a daemon: chef‐client ‐i 3600 ‐s 600 In this example, the client contacts the server every 3,600 seconds. The -s parameter lets you vary the period slightly. If you don’t set this, all of your clients might query the server rake roles In the web front end, you can assign roles to a node just like cookbooks using drag and drop. Freshly Stirred Ready-made recipes and cookbooks off the Internet will only cover standard application cases. For special cases, or individual configurations, you will typically need to create your own cookbook. The following, extremely simple example, creates a text file on the client called /tmp/thoughts.txt that is based on the quick_start cookbook [6], and it adds a sentence that is G Figure 4: The Status tab lists all the nodes with their last contact attempts and recipe assignments (following Run List). F Figure 3: Using drag and drop to assign recipes to a node. In this example, the client runs the beispiel recipe first, followed by emacs. 72 Admin 01 www.admin-magazine.com
Chef Management Figure 5: The client has picked up its assigned recipe from the server and executed it. This puts a preconfigured version of Emacs on its disk. generated dynamically in part. Start by creating a new cookbook called beispiel in chef-repo: rake new_cookbook COOKBOOK=beispiel The command creates a beispiel folder below cookbooks, populates it with the required subdirectories, then creates an empty recipe named default.rb. Before you start filling this with content, first create a template for the file you want to create, /tmp/thoughts. txt. This will later contain the sentence Thought for the day: and the recipe will append an ingenious thought on a daily basis. The complete template is thus: Thought for the day: The recipe will replace the wildcard with text later on. The new template needs to be in templates/default/; you can save it as thoughts.txt.erb. Most recipes use templates like this, or, to quote the developers: “We love templates.” Hand Mixer Now, compose a matching recipe that picks up the template and uses it to generate the /tmp/thoughts.txt file. To save work here, you can extend the existing, but empty, default.rb recipe in the recipes subdirectory. The recipe for this example looks like: template "/tmp/thoughts.txt" do source "thoughts.txt.erb" variables :thought => U node[:thought] action :create end This should be fairly self-explanatory for Ruby aficionados: It creates the /tmp/thoughts.txt file from the thoughts.txt.erb template and then replaces the wildcard with the content of the thought variable. Now you just need to think about what thoughts to use here. Spice In this example, thought will be an attribute. Attributes store node-specific settings in a cookbook for recipes to evaluate and use. A typical attribute would be, say, a command-line parameter for a program launched automatically by a recipe. The attributes are identical for each call to the recipe and, thus, no more than constants provided by the recipe author. In contrast to genuine Ruby constants, attributes can be modified via the web interface (in the window used to assign cookbooks to nodes). A cookbook groups all of the attributes in its attributes subdirectory. For the example here, you need to create a beispiel.rb file with the following content: thought "Silence is golden ..." Now you just need to register the new cookbook with the server rake upload_cookbooks and assign it to one or multiple nodes in the web front end. After running chef-client, the /tmp/thoughts.txt file should appear. This recipe leaves much scope for improvement. For example, you could randomly choose the thought of the day, which Ruby programmers should handle easily. Because recipes are full-fledged Ruby scripts, you can draw from the full scope of the language and on RubyGems. In the case of the latter, the recipe should first check to see whether the Gem exists on the client and, if not, install it. The beispiel/metadata.json file stores metadata on the new cookbook. Before you roll out the cookbook in a production environment, you might want to add some details. As the file extension suggests, the file uses the JSON format. Conclusions Chef is a complex piece of software, and once you have it running and have finished modifying or creating your recipes, it does make the administrator’s life much easier – at least on Linux systems. Unfortunately, the learning curve is very hard going for newcomers. The online documentation for Chef is fairly chaotic and incomplete [7]. If you need to know more about writing cookbooks, it is a good idea to download prebuilt examples and investigate them. The cookbook for emacs shows you how to use action :upgrade to install a package for example. Additionally, it is hard to find help or how-tos, even on the web, if you have a problem. Your best option here is to post your questions on the mailing list [8]. n Info [1] Installation guide: [http:// wiki. opscode. com/ display/ chef/ Installation] [2] RabbitMQ: [http:// www. rabbitmq. com/ server. html] [3] openSUSE build service for RabbitMQ: [http:// software. opensuse. org/ search? q=rabbitmq‐server& baseproject=openSUSE%3A11. 2] [4] Information on full-text searches in Chef: [http:// wiki. opscode. com/ display/ chef/ Search] [5] Repository with prebuilt cookbooks: [http:// cookbooks. opscode. com/] [6] Cookbook quick start: [http:// wiki. opscode. com/ display/ chef/ Cookbook+Quick+Start] [7] Chef wiki: [http:// wiki. opscode. com/ display/ chef/] [8] Chef mailing list: [http:// lists. opscode. com/ sympa/ lists/ opensource/ chef] www.admin-magazine.com Admin 01 73
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