add cloud-init-run-module and ec2init/execute.py

cloud-init-run-module handles some boilerplate code for running
items on a 'frequency'.  It has the following usefulness

- a config module can be put into ec2init dir and implement a 'run'
  method that takes a list of arguments and the path to a config file
- it handles invoking module.run() only at a given frequency
  This is similar to karmic's ec2init's "run_once_ever" or run_once_per_ami

execute.py is an example module that executes the arguments given to it

An example usage in an upstart job would be with a 'exec' line like:

   exec cloud-init-run-module once_per_ami clean-core execute rm /var/run/core

The above would then run the command 'rm /var/run/core' only once

3 files changed, 67 insertions, 1 deletions

diff --git a/cloud-init-run-module.py b/cloud-init-run-module.py
new file mode 100755
index 00000000..5a35de5d
--- /dev/null
+++ b/cloud-init-run-module.py
@@ -0,0 +1,50 @@
+#!/usr/bin/python
+
+import sys
+import ec2init
+
+def Usage(out = sys.stdout):
+    out.write("Usage: cloud-init-run-module freq sem-name mod-name [args]")
+    
+def main():
+    # expect to be called with
+    #   <freq> <semaphore-name> <module-name> args
+    if len(sys.argv) < 4:
+        Usage(sys.stderr)
+        sys.exit(1)
+
+    (freq,semname,modname)=sys.argv[1:4]
+    run_args=sys.argv[4:]
+
+    if ec2init.sem_has_run(semname,freq):
+        sys.stderr.write("%s already ran %s\n" % (semname,freq))
+        sys.exit(0)
+
+    try:
+        mod = __import__('ec2init.' + modname)
+        inst = getattr(mod,modname)
+    except:
+        sys.stderr.write("Failed to load module ec2init.%s\n" % modname)
+        sys.exit(1)
+
+    import os
+
+    cfg_path = None
+    cfg_env_name = "CLOUD_CFG"
+    if os.environ.has_key(cfg_env_name):
+        cfg_path = os.environ[cfg_env_name]
+
+    try:
+        if not ec2init.sem_acquire(semname,freq):
+            sys.stderr.write("Failed to acquire lock on %s\n" % semname)
+            sys.exit(1)
+
+        inst.run(run_args,cfg_path)
+    except:
+        ec2init.sem_clear(semname,freq)
+        raise
+
+    sys.exit(0)
+
+if __name__ == '__main__':
+    main()
diff --git a/ec2init/execute.py b/ec2init/execute.py
new file mode 100644
index 00000000..d7386663
--- /dev/null
+++ b/ec2init/execute.py
@@ -0,0 +1,14 @@
+def run(list,cfg):
+    import subprocess
+    subprocess.Popen(list).communicate()
+    retcode = subprocess.call(list)
+
+    if retcode == 0:
+        return
+
+    if retcode < 0:
+        str="Cmd terminated by signal %s\n" % -retcode
+    else:
+        str="Cmd returned %s\n" % retcode
+    str+=' '.join(list)
+    raise Exception(str)
diff --git a/setup.py b/setup.py
index aaa7cbeb..0f86cb54 100755
--- a/setup.py
+++ b/setup.py
@@ -36,7 +36,9 @@ setup(name='EC2-init',
                'ec2-set-hostname.py',
                'ec2-wait-for-meta-data-service.py',
                'ec2-init.py',
-               'ec2-is-compat-env'],
+               'ec2-is-compat-env',
+               'cloud-init-run-module.py'
+               ],
       data_files=[('/etc/ec2-init', ['ec2-config.cfg']),
                   ('/etc/ec2-init/templates', glob('templates/*')),
                   ('/etc/init', ['ec2init.conf']),