[chef] File Provider Changes in 11.6

Chronological Thread 
  • From: Daniel DeLeo < >
  • To: chef < >
  • Subject: [chef] File Provider Changes in 11.6
  • Date: Fri, 7 Jun 2013 14:35:00 -0700

(Gist form: https://gist.github.com/danielsdeleo/5732547#file-ft-announce-md)

Hi Chefs,

We've recently merged a substantial rewrite of Chef's file provider
family to master, and it will be released in 11.6.0. As part of these
changes, we've standardized the way the different providers create files
and update content, and added some cool improvements and features. But
first, a word of caution:

## Changes to Previously Undefined Behaviors

Prior to this patch, file providers did not have defined behavior for
some situations, but instead relied on the behavior of the underlying
ruby implementation. We feel that defining and standardizing this
behavior will be a huge benefit to you, but there is some risk of
breakage, so please read on:

* Chef previously did not define what file permissions it would set if a
  file resource did not specify them, and was inconsistent between
  different providers and in some cases differed based on the version of
  ruby used. All file providers will now create files with default
  permissions determined by the OS and filesystem default behavior. In
  general this is governed by your umask setting, but may also be affected
  by filesystem type or mount options.

  This can be a problem when depending on the default file mode when
  managing ssh keys or config with `cookbook_file` or `template`
  resources. In previous chef versions, `cookbook_file` would set the mode
  of a file to `0600` if not explicitly specified, and `template`
  resources would set the mode to `0600` if not specified when running
  on ruby 1.9.3, but `0644` on ruby 1.9.2 and earlier. In Chef 11.6,
  these are likely to be created with `0644` permissions (assuming a
  `022` umask), which can cause SSH operations to error out.

* Chef previously did not have a defined behavior if a file provider
  encountered something other than a file when attempting to update
  content. In particular, chef would follow symlinks and overwrite the
  symlink target's content; other dir entry types (such as devices, named
  pipes, etc.) would fail in strange ways. Chef will now raise an error
  instead of overwriting the content of a symlink. If you wish, you can
  delete whatever's in your way by setting `force_unlink true` on your
  resource. Note that there is no longer any built in means for managing
  the content of a file via a symlink--you must manage the target file

## Other Risks

File providers have been significantly refactored, with many methods
deprecated. If you've written custom providers that subclass a file
provider, we recommend you test them against master (or an upcoming beta
when available). We've made every effort to ensure that code using the
now-deprecated methods will continue to work, but it's possible that the
new code may not set internal state in a way your code expects.

## New Features and Enhancements

By rewriting the file providers to comprise a set of reusable
components, we're able to deliver a lot of enhancements we think you'll

* SELinux support: Chef will `restorecon` files after modifying them.
* Configurable atomic file updates. Chef lets you choose between atomic
  (mv-based) or non-atomic (cp-based) file updates. Defaults to atomic.
  * will not fail updating important file when out of disk space
  * will not fail updating a running binary
  * may alter file permissions when running as non-root user in some
  * files will temporarily have incorrect selinux permissions (until
    restorecon runs) or windows ACLs (until an ACL restore step runs)
  Non atomic is basically converse of the above.

  Global config: `file_atomic_update`, per-resource: `atomic_update`

  **NOTE:** At the moment, we don't know if this will automatically make
  community cookbooks work with selinux enabled; it's likely that the
  debian style file hierarchies used by some community cookbooks
  conflict with default selinux policy.

* All file providers will now create files such that ACL inheritance
  works as expected on Windows.
* Remote file can automatically send HTTP conditional GET requests,
  using ETags and If-Modified-Since. This is enabled by defualt, use
  `use_conditional_get false` to disable, or `use_etags false` or
  `use_last_modified false` to disable individual headers.
* Remote file now supports FTP and local files, using "ftp://" and
  "file://" URIs, respectively.
* Remote file supports custom headers.

### Template Helper Methods

Template resources can now define helper methods or modules for use in
the template context.

In the template resource, there are three interfaces to extend the
template context. The simplest way is to declare a single method inline,
like this:

template "/path" do

  # The classic "hello world"
  helper(:hello_world) { "hello world" }

  # You can reference the node object to clean up repeated calls to
  # your cookbook's attributes:
  helper(:app) { node["app"] }

  # Helpers can take arguments.
  helper(:app_conf) { |setting| node["app"][setting] }

Your template can then use the methods you've created like this:
Say hello: <%= hello_world %> 

node["app"]["listen_port"] is: <%= app["listen_port"] %>

node["app"]["log_location"] is: <%= app_conf("log_location") %>

If your logic gets more complicated or your dentist told you to avoid
syntax sugar, you can define a module inline instead. This may also be
handy as an intermediate step between the inline method syntax above and
the full-blown module approach below when refactoring. The following code
is functionally identical to the first example:

template "/path" do
  helpers do
    # Now you're in the context of a module that will extend your
    # template

    def hello_world
      "hello world"

    def app

    def app_conf(setting)

Finally, you can simply name a module to extend your template. If you
need to reuse extensions in multiple templates, or your template
extension code grows too unwieldy for the inline approaches above, you
can define a module in a library and use it in your templates like this:

template "/path" do

Daniel DeLeo

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