Chef Solo Automator Plugin

This section describes an automator that uses chef-solo. Basic knowledge of Chef and its primitives is assumed.


The Chef Solo Automator plugin, like all automator plugins, is responsible for performing the installation and operation of services on remote hosts. The Chef Solo Automator plugin achieves this by running chef-solo on the remote host with a custom run-list and set of JSON attributes. The attributes provided to each chef-solo run will be a combination of cluster-wide configuration attributes, as well as service-specific attributes definable for each action. Each chef-solo run is self-contained and intended to perform a specific task such as starting a service. This differs from the typical usage of Chef where one builds up a large run-list managing all resources on a box in one run.

To illustrate this, consider the following example which shows how we can manage the apache web server on Loom cluster nodes using the “apache2” community cookbook. We define a Loom service “apache-httpd” as follows:

    "dependson": [
    "description": "Apache HTTP Server",
    "name": "apache-httpd",
    "provisioner": {
        "actions": {
            "install": {
                "type": "chef-solo"
                "fields": {
                    "run_list": "recipe[apache2::default]",
            "configure": {
                "type": "chef-solo"
                "fields": {
                    "run_list": "recipe[apache2::default]",
            "start": {
                "type": "chef-solo"
                "fields": {
                    "json_attributes": "{\"loom\": { \"node\": { \"services\": { \"apache2\": \"start\" } } } }",
                    "run_list": "recipe[apache2::default],recipe[loom_service_runner::default]",
            "stop": {
                "type": "chef-solo"
                "fields": {
                    "json_attributes": "{\"loom\": { \"node\": { \"services\": { \"apache2\": \"stop\" } } } }",
                    "run_list": "recipe[apache2::default],recipe[loom_service_runner::default]",

For each action, we define the type, and the custom fields run_list and json_attributes. (defaults to empty string if not specified). The type field indicates to the provisioner to use the Chef Solo Automator plugin to manage this action. The run_list field specifies the run-list to use. The json_attributes field is any additional JSON data we wish to include in the Chef run (more on this later). When the Chef Solo Automator plugin executes any of these actions for the apache-httpd service, it performs the following actions:

  1. generate a task-specific JSON file containing any attributes defined in the json_attributes field, as well as base cluster attributes defined elsewhere in Continuuity Loom.
  2. invoke chef-solo using the run_list field as the run-list as follows: chef-solo -o [run_list] -j [task-specific json]

In this example, to execute an “install” task for the apache-httpd service, the provisioner will simply run the default recipe from the apache2 cookbook as a single chef-solo run. No additional JSON attributes are provided beyond the base cluster configuration attributes.

For a “configure” task, the provisioner will also run the default recipe from the apache2 cookbook. For this community cookbook, the installation and configuration are done in the same recipe, which is common but not always the case. So one may wonder why we need both ‘install’ and ‘configure’ when they perform identical actions. It is best practice to keep them both, since configure may be run many times throughout the lifecycle of the cluster, and install is needed to satisfy dependencies.

The “start” and “stop” tasks introduce a couple of features. They make use of the json_attributes field to specify custom JSON attributes. Note that the format is an escaped JSON string. The run_list field also contains an additional recipe, loom_service_runner::default. More on this later, but essentially this is a helper cookbook that can operate on any Chef service resource. It looks for any service names listed in node[‘loom’][‘node’][‘services’], finds the corresponding Chef service resource, and invokes the specified action.

JSON Attributes

Continuuity Loom maintains significant JSON data for a cluster, and makes it available for each task. This JSON data includes:
  • cluster-wide configuration defined in cluster templates (Catalog -> cluster template -> defaults -> config)
  • node data for each node of the cluster: hostname, ip, etc
  • service data, specified in the actions for each service

The Chef Solo Automator plugin automatically merges this data into a single JSON file, which is then passed to chef-solo via the --json-attributes argument. Any custom cookbooks that want to make use of this Loom data need to be familiar with the JSON layout of the Loom data. In brief, cluster-wide configuration defined in cluster templates and service-level action data are merged together, and preserved at the top-level. Loom data is then also merged in under loom/*. For example:

    // cluster config attributes defined in clustertemplates are preserved here at top-level
    // service-level action data string converted to json and merged here at top-level
    "loom": {
        "clusterId": "00000001",
        "cluster": {
            //cluster config here as well
            "nodes": {
                // node data
        "services": [
          // list of loom services on this node
Consider the following two rules of thumb:
  • When using community cookbooks, attributes can be specified in Loom templates exactly as the cookbook expects (at the top-level).
  • When writing cookbooks specifically utilizing Loom metadata (cluster node data for example), recipes can access the metadata at node['loom']['cluster']...


Each Loom Automator plugin is responsible for implementing a bootstrap method in which it performs any actions it needs to be able to carry out further tasks. The Chef Solo Automator plugin performs the following actions for a bootstrap task:
  1. Bundle its local copy of the cookbooks/roles/data_bags directories into tarballs, cookbooks.tar.gz, roles.tar.gz, data_bags.tar.gz.
    • Unless the tarballs exist already and were created in the last 10 minutes.
  2. Logs into the remote box and installs chef via the Opscode Omnibus installer (curl -L | bash).

  3. Creates the remote loom cache directory /var/cache/loom.

  4. SCP the local tarballs to the remote Loom cache directory.

  5. Extracts the tarballs on the remote host to the default chef directory /var/chef.

The most important things to note are that:
  • Upon adding any new cookbooks, roles, or data_bags to the local directories, the tarballs will be regenerated within 10 minutes and used by all running provisioners.
  • This implementation requires internet access to install Chef (and also required by the cookbooks used within).

Adding your own Cookbooks

Cookbook requirements

Since the Chef Solo Automator plugin is implemented using chef-solo, the following restrictions apply:

  • No Chef search capability
  • No persistent attributes

Cookbooks should be fully attribute-driven. At this time the Chef Solo Automator does not support the chef-solo “environment” primitive. Attributes normally specified in an environment can instead be populated in Loom primitives such as cluster templates or service action data.

In order to add cookbooks, roles, or data-bags for use by the provisioners, simply add them to the local chef directories for the Chef Solo Automator plugin. If using the default package install, these directories are currently:


Your cookbook should be readable by the ‘loom-provisioner’ user (default: ‘loom’). The next provisioner which runs a bootstrap task will regenerate the local tarballs (for example /opt/loom/provisioner/daemon/plugins/automators/chef_solo_automator/chef_solo_automator/cookbooks.tar.gz) and it will be available for use when chef-solo runs on the remote box.

In order to actually invoke your cookbook or role as part of a cluster provision, you will need to define a Loom service definition with the following parameters:

  • Category: any action (install, configure, start, stop, etc)
  • Type: chef-solo
  • run_list: a run-list containing your cookbook’s recipe(s) or roles. If your recipe depends on resources defined in other cookbooks which aren’t declared dependencies in your cookbook’s metadata, make sure to also add them to the run-list.
  • json_attributes: (optional), any additional custom attributes you want to specify, unique to this action

Then simply add your service to a cluster template.

Helper Cookbooks

Continuuity Loom ships with several helper cookbooks.


This is a convenience cookbook which is intended to provide base functionality for all hosts provisioned by loom. It currently does the following:

  • run apt-get update (on Ubuntu hosts)
  • include loom_hosts::default (discussed below)
  • include loom_firewall::default (discussed below)
  • include ulimit::default to enable user-defined ulimits


This simple cookbook’s only purpose is to populate /etc/hosts with the hostnames and IP addresses of the cluster. It achieves this by accessing the loom-populated attributes at node['loom']['cluster']['nodes'] to get a list of all the nodes in the cluster. It then simply utilizes the community “hostsfile” cookbook’s LWRP to write entries for each node.

The example loom service definition invoking this cookbook is called “base”. It simply sets up a “configure” service action of type “chef-solo” and run_list recipe[loom_base::default] (which includes recipe[loom_hosts::default]). Note that the community “hostsfile” cookbook is not needed in the run-list since it is declared in loom_hosts’s metadata.


This cookbook comes in handy as a simple way to isolate the starting and stopping of various services within your cluster. It allows you to simply specify the name of a Chef service resource and an action within a Loom service definition. When run, it will simply lookup the Chef service resource of the given name, regardless of which cookbook it is defined in, and run the given action. In the example apache-httpd service definition above, it is simply included in the run-list to start or stop the apache2 service defined in the apache2 community cookbook. All that is needed is to set the following attribute to “start” or “stop”:

node['loom']['node']['services']['apache2'] = "start"


This cookbook is a simple iptables firewall manager, with the added functionality of automatically whitelisting all nodes of a cluster. To use, simply set any of the following attributes:

node['loom_firewall']['INPUT_policy']  = (string)
node['loom_firewall']['FORWARD_policy'] = (string)
node['loom_firewall']['OUTPUT_policy'] = (string)
node['loom_firewall']['notrack_ports'] = [ array ]
node['loom_firewall']['open_tcp_ports'] = [ array ]
node['loom_firewall']['open_udp_ports'] = [ array ]

If this recipe is included in the run-list and no attributes specified, the default behavior is to disable the firewall.

Best Practices

  • Continuuity Loom is designed to use attribute-driven cookbooks. All user-defined attributes are specified in Loom primitives. Recipes that use Chef server capabilities like discovery and such do not operate well with Continuuity Loom.
  • Separate the install, configuration, initialization, starting/stopping, and deletion logic of your cookbooks into granular recipes. This way Loom services can often be defined with a 1:1 mapping to recipes. Remember that Continuuity Loom will need to install, configure, initialize, start, stop, and remove your services, each independently through a combination of run-list and attributes.
  • Use wrapper cookbooks in order to customize community cookbooks to suit your needs.
  • Remember to declare cookbook dependencies in metadata.