Passing a Fabric env.hosts sting as a variable is not work in function

Question

Passing a Fabric env.hosts sting as a variable is not work in function.

demo.py

#!/usr/bin/env python

from fabric.api import env, run

def deploy(hosts, command):
    print hosts
    env.hosts = hosts
    run(command)

main.py

#!/usr/bin/env python

from demo import deploy

hosts = ['localhost']
command = 'hostname'
deploy(hosts, command)

python main.py

['localhost']
No hosts found. Please specify (single) host string for connection:

But env.host_string works!

demo.py

#!/usr/bin/env python

from fabric.api import env, run

def deploy(host, command):
  print host
  env.host_string = host
  run(command)

main.py

#!/usr/bin/env python

from demo import deploy

host = 'localhost'
command = 'hostname'
deploy(host, command)

python main.py

localhost
[localhost] run: hostname
[localhost] out: heydevops-workspace

But the env.host_string is not enough for us, it's a single host. Maybe we can use env.host_string within a loop, but that's not good. Because we also want to set the concurrent tasks number and run them parallelly.

Now in ddep(my deployment engine), I only use MySQLdb to get the parameters then execute the fab command like:

os.system("fab -f service/%s.py -H %s -P -z %s %s" % (project,host,number,task))

This is a simple way but not good. Because if I use the fab command, I can't catch the exceptions and failures of the results in Python, to make my ddep can "retry" the failed hosts. If I use the "from demo import deploy", I can control and get them by some codes in Python.

So now "env.host " is the trouble. Can somebody give me a solution? Thanks a lot.

Answer 1

Here's my insight.

According to docs, if you're calling fabric tasks from python scripts - you should use fabric.tasks.execute.

Should be smth like this:

• demo.py

  from fabric.api import run
  from fabric.tasks import execute
  
  
  def deploy(hosts, command):
      execute(execute_deploy, command=command, hosts=hosts)
  
  
  def execute_deploy(command):
      run(command)
  

• main.py

  from demo import deploy
  
  hosts = ['localhost']
  command = 'hostname'
  
  deploy(hosts, command)
  

Then, just run python main.py. Hope that helps.