chef: Add option to pin chef omnibus install version

Most users of chef will want to pin the version that is installed.
Typically new versions of chef have to be evaluated for breakage etc.

This change proposes a new optional `omnibus_version` field to the chef
configuration. The changeset also adds documentation referencing the new
field.

LP: #1462693

2 files changed, 58 insertions, 12 deletions

diff --git a/cloudinit/config/cc_chef.py b/cloudinit/config/cc_chef.py
index c192dd32..46abedd1 100644
--- a/cloudinit/config/cc_chef.py
+++ b/cloudinit/config/cc_chef.py
@@ -58,6 +58,9 @@ file).
       log_level:
       log_location:
       node_name:
+      omnibus_url:
+      omnibus_url_retries:
+      omnibus_version:
       pid_file:
       server_url:
       show_time:
@@ -71,7 +74,6 @@ import itertools
 import json
 import os
 
-from cloudinit import temp_utils
 from cloudinit import templater
 from cloudinit import url_helper
 from cloudinit import util
@@ -280,6 +282,31 @@ def run_chef(chef_cfg, log):
     util.subp(cmd, capture=False)
 
 
+def install_chef_from_omnibus(url=None, retries=None, omnibus_version=None):
+    """Install an omnibus unified package from url.
+
+    @param url: URL where blob of chef content may be downloaded. Defaults to
+        OMNIBUS_URL.
+    @param retries: Number of retries to perform when attempting to read url.
+        Defaults to OMNIBUS_URL_RETRIES
+    @param omnibus_version: Optional version string to require for omnibus
+        install.
+    """
+    if url is None:
+        url = OMNIBUS_URL
+    if retries is None:
+        retries = OMNIBUS_URL_RETRIES
+
+    if omnibus_version is None:
+        args = []
+    else:
+        args = ['-v', omnibus_version]
+    content = url_helper.readurl(url=url, retries=retries).contents
+    return util.subp_blob_in_tempfile(
+        blob=content, args=args,
+        basename='chef-omnibus-install', capture=False)
+
+
 def install_chef(cloud, chef_cfg, log):
     # If chef is not installed, we install chef based on 'install_type'
     install_type = util.get_cfg_option_str(chef_cfg, 'install_type',
@@ -298,17 +325,11 @@ def install_chef(cloud, chef_cfg, log):
         # This will install and run the chef-client from packages
         cloud.distro.install_packages(('chef',))
     elif install_type == 'omnibus':
-        # This will install as a omnibus unified package
-        url = util.get_cfg_option_str(chef_cfg, "omnibus_url", OMNIBUS_URL)
-        retries = max(0, util.get_cfg_option_int(chef_cfg,
-                                                 "omnibus_url_retries",
-                                                 default=OMNIBUS_URL_RETRIES))
-        content = url_helper.readurl(url=url, retries=retries).contents
-        with temp_utils.tempdir() as tmpd:
-            # Use tmpdir over tmpfile to avoid 'text file busy' on execute
-            tmpf = "%s/chef-omnibus-install" % tmpd
-            util.write_file(tmpf, content, mode=0o700)
-            util.subp([tmpf], capture=False)
+        omnibus_version = util.get_cfg_option_str(chef_cfg, "omnibus_version")
+        install_chef_from_omnibus(
+            url=util.get_cfg_option_str(chef_cfg, "omnibus_url"),
+            retries=util.get_cfg_option_int(chef_cfg, "omnibus_url_retries"),
+            omnibus_version=omnibus_version)
     else:
         log.warn("Unknown chef install type '%s'", install_type)
         run = False
diff --git a/cloudinit/util.py b/cloudinit/util.py
index ae5cda8d..7e9d94fc 100644
--- a/cloudinit/util.py
+++ b/cloudinit/util.py
@@ -1742,6 +1742,31 @@ def delete_dir_contents(dirname):
             del_file(node_fullpath)
 
 
+def subp_blob_in_tempfile(blob, *args, **kwargs):
+    """Write blob to a tempfile, and call subp with args, kwargs. Then cleanup.
+
+    'basename' as a kwarg allows providing the basename for the file.
+    The 'args' argument to subp will be updated with the full path to the
+    filename as the first argument.
+    """
+    basename = kwargs.pop('basename', "subp_blob")
+
+    if len(args) == 0 and 'args' not in kwargs:
+        args = [tuple()]
+
+    # Use tmpdir over tmpfile to avoid 'text file busy' on execute
+    with temp_utils.tempdir() as tmpd:
+        tmpf = os.path.join(tmpd, basename)
+        if 'args' in kwargs:
+            kwargs['args'] = [tmpf] + list(kwargs['args'])
+        else:
+            args = list(args)
+            args[0] = [tmpf] + args[0]
+
+        write_file(tmpf, blob, mode=0o700)
+        return subp(*args, **kwargs)
+
+
 def subp(args, data=None, rcs=None, env=None, capture=True, shell=False,
          logstring=False, decode="replace", target=None, update_env=None):