# Copyright (C) 2011 Internet Systems Consortium, Inc. ("ISC")
#
# Permission to use, copy, modify, and distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SYSTEMS CONSORTIUM
# DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL
# INTERNET SYSTEMS CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT,
# INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING
# FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
# NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
# WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
"""
Module for managing components (abstraction of process). It allows starting
them in given order, handling when they crash (what happens depends on kind
of component) and shutting down. It also handles the configuration of this.
Dependencies between them are not yet handled. It might turn out they are
needed, in that case they will be added sometime in future.
This framework allows for a single process to be started multiple times (by
specifying multiple components with the same configuration). However, the rest
of the system might not handle such situation well, so until it is made so,
it would be better to start each process at most once.
"""
import isc.log
from isc.log_messages.bind10_messages import *
import time
logger = isc.log.Logger("boss")
DBG_TRACE_DATA = 20
DBG_TRACE_DETAILED = 80
START_CMD = 'start'
STOP_CMD = 'stop'
STARTED_OK_TIME = 10
STATE_DEAD = 'dead'
STATE_STOPPED = 'stopped'
STATE_RUNNING = 'running'
class Component:
"""
This represents a single component. It has some defaults of behaviour,
which should be reasonable for majority of ordinary components, but
it might be inherited and modified for special-purpose components,
like the core modules with different ways of starting up. Another
way to tweak only the start of the component (eg. by providing some
command line parameters) is to set _start_func function from within
inherited class.
The methods are marked if it is expected for them to be overridden.
The component is in one of the three states:
- Stopped - it is either not started yet or it was explicitly stopped.
The component is created in this state (it must be asked to start
explicitly).
- Running - after start() was called, it started successfully and is
now running.
- Dead - it failed and can not be resurrected.
Init
| stop()
| +-----------------------+
| | |
v | start() success |
Stopped --------+--------> Running <----------+
| | |
|failure | failed() |
| | |
v | |
+<-----------+ |
| |
| kind == dispensable or kind|== needed and failed late
+-----------------------------+
|
| kind == core or kind == needed and it failed too soon
v
Dead
Note that there are still situations which are not handled properly here.
We don't recognize a component that is starting up, but not ready yet, one
that is already shutting down, impossible to stop, etc. We need to add more
states in future to handle it properly.
"""
def __init__(self, process, boss, kind, address=None, params=None):
"""
Creates the component in not running mode.
The parameters are:
- `process` is the name of the process to start.
- `boss` the boss object to plug into. The component needs to plug
into it to know when it failed, etc.
- `kind` is the kind of component. It may be one of:
* 'core' means the system can't run without it and it can't be
safely restarted. If it does not start, the system is brought
down. If it crashes, the system is turned off as well (with
non-zero exit status).
* 'needed' means the system is able to restart the component,
but it is vital part of the service (like auth server). If
it fails to start or crashes in less than 10s after the first
startup, the system is brought down. If it crashes later on,
it is restarted.
* 'dispensable' means the component should be running, but if it
doesn't start or crashes for some reason, the system simply tries
to restart it and keeps running.
- `address` is the address on message bus. It is used to ask it to
shut down at the end. If you specialize the class for a component
that is shut down differently, it might be None.
- `params` is a list of parameters to pass to the process when it
starts. It is currently unused and this support is left out for
now.
"""
if kind not in ['core', 'needed', 'dispensable']:
raise ValueError('Component kind can not be ' + kind)
self.__state = STATE_STOPPED
# These should be read-only
self._kind = kind
self._boss = boss
self._process = process
# This can be overwritten/set by the child classes
self._start_func = None
self._address = address
self._params = params
# These should be considered private. It is protected to
# allow tests in and for really rare ocassions, but a care
# should be taken to understand the Component code.
#
# It should not be accessed when the component wasn't run
# yet.
self._procinfo = None
def start(self):
"""
Start the component for the first time or restart it. If you need to
modify the way a component is started, do not replace this method,
but _start_internal. This one does some more bookkeeping around.
If you try to start an already running component, it raises ValueError.
"""
if self.__state == STATE_DEAD:
raise ValueError("Can't resurrect already dead component")
if self.running():
raise ValueError("Can't start already running component")
logger.info(BIND10_COMPONENT_START, self.name())
self.__state = STATE_RUNNING
self.__start_time = time.time()
try:
self._start_internal()
except Exception as e:
logger.error(BIND10_COMPONENT_START_EXCEPTION, self.name(), e)
self.failed(None)
raise
def _start_internal(self):
"""
This method does the actual starting of a process. If you need to
change the way the component is started, replace this method.
You can change the "core" of this function by setting self._start_func
to a function without parameters. Such function should start the
process and return the procinfo object describing the running process.
If you don't provide the _start_func, the usual startup by calling
boss.start_simple is performed.
If you override the method completely, you should consider overriding
pid, _stop_internal (and possibly _failed_internal and name) and kill
as well. You should also register any processes started within boss.
(In fact, you could set the _procinfo variable and use the provided
ones, but then you are OK with providing _start_func anyway).
The ability to override this method presents some flexibility. It
allows processes started in a strange way, as well as components that
have no processes at all or components with multiple processes (in case
of multiple processes, care should be taken to make their
started/stopped state in sync and all the processes that can fail
should be registered).
"""
# This one is not tested. For one, it starts a real process
# which is out of scope of unit tests, for another, it just
# delegates the starting to other function in boss (if a derived
# class does not provide an override function), which is tested
# by use.
if self._start_func is not None:
procinfo = self._start_func()
else:
# TODO Handle params, etc
procinfo = self._boss.start_simple(self._process)
self._procinfo = procinfo
self._boss.register_process(self.pid(), self)
def stop(self):
"""
Stop the component. If you need to modify the way a component is
stopped, do not replace this method, but _stop_internal. This one
does some more bookkeeping.
If you try to stop a component that is not running, it raises
ValueError.
"""
# This is not tested. It talks with the outher world, which is out
# of scope of unittests.
if not self.running():
raise ValueError("Can't stop a component which is not running")
logger.info(BIND10_COMPONENT_STOP, self.name())
self.__state = STATE_STOPPED
self._stop_internal()
def _stop_internal(self):
"""
This is the method that does the actual stopping of a component.
You can replace this method if you want a different way to do it.
If you're overriding this one, you probably want to replace the
_start_internal, kill and pid methods (and maybe _failed_internal and
name as well).
Also, note that it is a bad idea to raise exceptions from here.
Under such circumstance, the component will be considered stopped,
and the exception propagated, but we can't be sure it really is
dead.
"""
self._boss.stop_process(self._process, self._address)
# TODO Some way to wait for the process that doesn't want to
# terminate and kill it would prove nice (or add it to boss somewhere?)
def failed(self, exit_code):
"""
Notify the component it crashed. This will be called from boss object.
If you try to call failed on a component that is not running,
a ValueError is raised.
If it is a core component or needed component and it was started only
recently, the component will become dead and will ask the boss to shut
down with error exit status. A dead component can't be started again.
Otherwise the component will try to restart.
The exit code is used for logging. It might be None.
"""
logger.error(BIND10_COMPONENT_FAILED, self.name(), self.pid(),
exit_code if exit_code is not None else "unknown")
if not self.running():
raise ValueError("Can't fail component that isn't running")
self.__state = STATE_STOPPED
self._failed_internal()
# If it is a core component or the needed component failed to start
# (including it stopped really soon)
if self._kind == 'core' or \
(self._kind == 'needed' and time.time() - STARTED_OK_TIME <
self.__start_time):
self.__state = STATE_DEAD
logger.fatal(BIND10_COMPONENT_UNSATISFIED, self.name())
self._boss.component_shutdown(1)
# This means we want to restart
else:
logger.warn(BIND10_COMPONENT_RESTART, self.name())
self.start()
def _failed_internal(self):
"""
This method is called from failed. You can replace it if you need
some specific behaviour when the component crashes. The default
implementation is empty.
Do not raise exceptions from here, please. The propper shutdown
would have not happened.
"""
pass
def running(self):
"""
Informs if the component is currently running. It assumes the failed
is called whenever the component really fails and there might be some
time in between actual failure and the call.
It is not expected for this method to be overriden.
"""
return self.__state == STATE_RUNNING
def name(self):
"""
Returns human-readable name of the component. This is usually the
name of the executable, but it might be something different in a
derived class (in case it is overriden).
"""
return self._process
def pid(self):
"""
Provides a PID of a process, if the component is real running process.
This implementation expects it to be a real process, but derived class
may return None in case the component is something else.
This returns None in case it is not yet running.
You probably want to override this method if you're providing custom
_start_internal.
Note that some components preserve the pid after a call to stop or
failed. This is because the components need to preserve it in order
to be able to kill the process if it failed to stop properly. Therefore
you should not rely on the pid being None if the component is stopped.
"""
return self._procinfo.pid if self._procinfo is not None else None
def kill(self, forcefull=False):
"""
The component should be forcefully killed. This does not change the
internal state, it just kills the external process and expects a
failure to be reported when the process really dies.
If it isn't running, it does nothing.
If the forcefull is true, it uses SIGKILL instead of SIGTERM.
"""
if self._procinfo is not None:
if forcefull:
self._procinfo.process.kill()
else:
self._procinfo.process.terminate()
class Configurator:
"""
This thing keeps track of configuration changes and starts and stops
components as it goes. It also handles the inital startup and final
shutdown.
Note that this will allow you to stop (by invoking reconfigure) a core
component. There should be some kind of layer protecting users from ever
doing so (users must not stop the config manager, message queue and stuff
like that or the system won't start again). However, if a user specifies
b10-auth as core, it is safe to stop that one.
The parameters are:
* `boss`: The boss we are managing for.
* `specials`: Dict of specially started components. Each item is a class
representing the component.
The configuration passed to it (by startup() and reconfigure()) is a
dictionary, each item represents one component that should be running.
The key is an unique identifier used to reference the component. The
value is a dictionary describing the component. All items in the
description is optional unless told otherwise and they are as follows:
* `special` - Some components are started in a special way. If it is
present, it specifies which class from the specials parameter should
be used to create the component. In that case, some of the following
items might be irrelevant, depending on the special component choosen.
If it is not there, the basic Component class is used.
* `process` - Name of the executable to start. If it is not present,
it defaults to the identifier of the component.
* `kind` - The kind of component, either of 'core', 'needed' and
'dispensable'. This specifies what happens if the component fails.
This one is required.
* `address` - The address of the component on message bus. It is used
to shut down the component. All special components currently either
know their own address or don't need one and ignore it. The common
components should provide this.
* `params` - The command line parameters of the executable. Defaults
to no parameters. It is currently unused.
* `priority` - When starting the component, the components with higher
priority are started before the ones with lower priority. If it is
not present, it defaults to 0.
"""
def __init__(self, boss, specials = {}):
"""
Initializes the configurator, but nothing is started yet.
The boss parameter is the boss object used to start and stop processes.
"""
self.__boss = boss
# These could be __private, but as we access them from within unittest,
# it's more comfortable to have them just _protected.
# They are tuples (configuration, component)
self._components = {}
self._running = False
self.__specials = specials
def __reconfigure_internal(self, old, new):
"""
Does a switch from one configuration to another.
"""
self._run_plan(self._build_plan(old, new))
def startup(self, configuration):
"""
Starts the first set of processes. This configuration is expected
to be hardcoded from the boss itself to start the configuration
manager and other similar things.
"""
if self._running:
raise ValueError("Trying to start the component configurator " +
"twice")
logger.info(BIND10_CONFIGURATOR_START)
self.__reconfigure_internal(self._components, configuration)
self._running = True
def shutdown(self):
"""
Shuts everything down.
It is not expected that anyone would want to shutdown and then start
the configurator again, so we don't explicitly make sure that would
work. However, we are not avare of anything that would make it not
work either.
"""
if not self._running:
raise ValueError("Trying to shutdown the component " +
"configurator while it's not yet running")
logger.info(BIND10_CONFIGURATOR_STOP)
self._running = False
self.__reconfigure_internal(self._components, {})
def reconfigure(self, configuration):
"""
Changes configuration from the current one to the provided. It
starts and stops all the components as needed (eg. if there's
a component that was not in the original configuration, it is
started, any component that was in the old and is not in the
new one is stopped).
"""
if not self._running:
raise ValueError("Trying to reconfigure the component " +
"configurator while it's not yet running")
logger.info(BIND10_CONFIGURATOR_RECONFIGURE)
self.__reconfigure_internal(self._components, configuration)
def _build_plan(self, old, new):
"""
Builds a plan how to transfer from the old configuration to the new
one. It'll be sorted by priority and it will contain the components
(already created, but not started). Each command in the plan is a dict,
so it can be extended any time in future to include whatever
parameters each operation might need.
Any configuration problems are expected to be handled here, so the
plan is not yet run.
"""
logger.debug(DBG_TRACE_DATA, BIND10_CONFIGURATOR_BUILD, old, new)
plan = []
# Handle removals of old components
for cname in old.keys():
if cname not in new:
component = self._components[cname][1]
if component.running():
plan.append({
'command': STOP_CMD,
'component': component,
'name': cname
})
# Handle transitions of configuration of what is here
for cname in new.keys():
if cname in old:
for option in ['special', 'process', 'kind', 'address',
'params']:
if new[cname].get(option) != old[cname][0].get(option):
raise NotImplementedError('Changing configuration of' +
' a running component is ' +
'not yet supported. Remove' +
' and re-add ' + cname +
' to get the same effect')
# Handle introduction of new components
plan_add = []
for cname in new.keys():
if cname not in old:
component_config = new[cname]
creator = Component
if 'special' in component_config:
# TODO: Better error handling
creator = self.__specials[component_config['special']]
component = creator(component_config.get('process', cname),
self.__boss, component_config['kind'],
component_config.get('address'),
component_config.get('params'))
priority = component_config.get('priority', 0)
# We store tuples, priority first, so we can easily sort
plan_add.append((priority, {
'component': component,
'command': START_CMD,
'name': cname,
'config': component_config
}))
# Push the starts there sorted by priority
plan.extend([command for (_, command) in sorted(plan_add,
reverse=True,
key=lambda command:
command[0])])
return plan
def running(self):
"""
Returns if the configurator is running (eg. was started by startup and
not yet stopped by shutdown).
"""
return self._running
def _run_plan(self, plan):
"""
Run a plan, created beforehand by _build_plan.
With the start and stop commands, it also adds and removes components
in _components.
Currently implemented commands are:
* start
* stop
The plan is a list of tasks, each task is a dictionary. It must contain
at last 'component' (a component object to work with) and 'command'
(the command to do). Currently, both existing commands need 'name' of
the component as well (the identifier from configuration). The 'start'
one needs the 'config' to be there, which is the configuration description
of the component.
"""
done = 0
try:
logger.debug(DBG_TRACE_DATA, BIND10_CONFIGURATOR_RUN, len(plan))
for task in plan:
component = task['component']
command = task['command']
logger.debug(DBG_TRACE_DETAILED, BIND10_CONFIGURATOR_TASK,
command, component.name())
if command == START_CMD:
component.start()
self._components[task['name']] = (task['config'],
component)
elif command == STOP_CMD:
if component.running():
component.stop()
del self._components[task['name']]
else:
# Can Not Happen (as the plans are generated by ourselves).
# Therefore not tested.
raise NotImplementedError("Command unknown: " + command)
done += 1
except:
logger.error(BIND10_CONFIGURATOR_PLAN_INTERRUPTED, done, len(plan))
raise