From e6918187568dbd01842d8d1d2c808ce16a894239 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 21 Apr 2024 13:54:28 +0200 Subject: Adding upstream version 18.2.2. Signed-off-by: Daniel Baumann --- doc/mgr/modules.rst | 735 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 735 insertions(+) create mode 100644 doc/mgr/modules.rst (limited to 'doc/mgr/modules.rst') diff --git a/doc/mgr/modules.rst b/doc/mgr/modules.rst new file mode 100644 index 000000000..667664139 --- /dev/null +++ b/doc/mgr/modules.rst @@ -0,0 +1,735 @@ + + +.. _mgr-module-dev: + +ceph-mgr module developer's guide +================================= + +.. warning:: + + This is developer documentation, describing Ceph internals that + are only relevant to people writing ceph-mgr modules. + +Creating a module +----------------- + +In pybind/mgr/, create a python module. Within your module, create a class +that inherits from ``MgrModule``. For ceph-mgr to detect your module, your +directory must contain a file called `module.py`. + +The most important methods to override are: + +* a ``serve`` member function for server-type modules. This + function should block forever. +* a ``notify`` member function if your module needs to + take action when new cluster data is available. +* a ``handle_command`` member function if your module + exposes CLI commands. But this approach for exposing commands + is deprecated. For more details, see :ref:`mgr-module-exposing-commands`. + +Some modules interface with external orchestrators to deploy +Ceph services. These also inherit from ``Orchestrator``, which adds +additional methods to the base ``MgrModule`` class. See +:ref:`Orchestrator modules ` for more on +creating these modules. + +Installing a module +------------------- + +Once your module is present in the location set by the +``mgr module path`` configuration setting, you can enable it +via the ``ceph mgr module enable`` command:: + + ceph mgr module enable mymodule + +Note that the MgrModule interface is not stable, so any modules maintained +outside of the Ceph tree are liable to break when run against any newer +or older versions of Ceph. + +.. _mgr module dev logging: + +Logging +------- + +Logging in Ceph manager modules is done as in any other Python program. Just +import the ``logging`` package and get a logger instance with the +``logging.getLogger`` function. + +Each module has a ``log_level`` option that specifies the current Python +logging level of the module. +To change or query the logging level of the module use the following Ceph +commands:: + + ceph config get mgr mgr//log_level + ceph config set mgr mgr//log_level + +The logging level used upon the module's start is determined by the current +logging level of the mgr daemon, unless if the ``log_level`` option was +previously set with the ``config set ...`` command. The mgr daemon logging +level is mapped to the module python logging level as follows: + +* <= 0 is CRITICAL +* <= 1 is WARNING +* <= 4 is INFO +* <= +inf is DEBUG + +We can unset the module log level and fallback to the mgr daemon logging level +by running the following command:: + + ceph config set mgr mgr//log_level '' + +By default, modules' logging messages are processed by the Ceph logging layer +where they will be recorded in the mgr daemon's log file. +But it's also possible to send a module's logging message to it's own file. + +The module's log file will be located in the same directory as the mgr daemon's +log file with the following name pattern:: + + ..log + +To enable the file logging on a module use the following command:: + + ceph config set mgr mgr//log_to_file true + +When the module's file logging is enabled, module's logging messages stop +being written to the mgr daemon's log file and are only written to the +module's log file. + +It's also possible to check the status and disable the file logging with the +following commands:: + + ceph config get mgr mgr//log_to_file + ceph config set mgr mgr//log_to_file false + + + +.. _mgr-module-exposing-commands: + +Exposing commands +----------------- + +There are two approaches for exposing a command. The first method involves using +the ``@CLICommand`` decorator to decorate the methods needed to handle a command. +The second method uses a ``COMMANDS`` attribute defined for the module class. + + +The CLICommand approach +~~~~~~~~~~~~~~~~~~~~~~~ + +.. code:: python + + @CLICommand('antigravity send to blackhole', + perm='rw') + def send_to_blackhole(self, oid: str, blackhole: Optional[str] = None, inbuf: Optional[str] = None): + ''' + Send the specified object to black hole + ''' + obj = self.find_object(oid) + if obj is None: + return HandleCommandResult(-errno.ENOENT, stderr=f"object '{oid}' not found") + if blackhole is not None and inbuf is not None: + try: + location = self.decrypt(blackhole, passphrase=inbuf) + except ValueError: + return HandleCommandResult(-errno.EINVAL, stderr='unable to decrypt location') + else: + location = blackhole + self.send_object_to(obj, location) + return HandleCommandResult(stdout=f"the black hole swallowed '{oid}'") + +The first parameter passed to ``CLICommand`` is the "name" of the command. +Since there are lots of commands in Ceph, we tend to group related commands +with a common prefix. In this case, "antigravity" is used for this purpose. +As the author is probably designing a module which is also able to launch +rockets into the deep space. + +The `type annotations `_ for the +method parameters are mandatory here, so the usage of the command can be +properly reported to the ``ceph`` CLI, and the manager daemon can convert +the serialized command parameters sent by the clients to the expected type +before passing them to the handler method. With properly implemented types, +one can also perform some sanity checks against the parameters! + +The names of the parameters are part of the command interface, so please +try to take the backward compatibility into consideration when changing +them. But you **cannot** change name of ``inbuf`` parameter, it is used +to pass the content of the file specified by ``ceph --in-file`` option. + +The docstring of the method is used for the description of the command. + +The manager daemon cooks the usage of the command from these ingredients, +like:: + + antigravity send to blackhole [] Send the specified object to black hole + +as part of the output of ``ceph --help``. + +In addition to ``@CLICommand``, you could also use ``@CLIReadCommand`` or +``@CLIWriteCommand`` if your command only requires read permissions or +write permissions respectively. + + +The COMMANDS Approach +~~~~~~~~~~~~~~~~~~~~~ + +This method uses the ``COMMANDS`` class attribute of your module to define +a list of dicts like this:: + + COMMANDS = [ + { + "cmd": "foobar name=myarg,type=CephString", + "desc": "Do something awesome", + "perm": "rw", + # optional: + "poll": "true" + } + ] + +The ``cmd`` part of each entry is parsed in the same way as internal +Ceph mon and admin socket commands (see mon/MonCommands.h in +the Ceph source for examples). Note that the "poll" field is optional, +and is set to False by default; this indicates to the ``ceph`` CLI +that it should call this command repeatedly and output results (see +``ceph -h`` and its ``--period`` option). + +Each command is expected to return a tuple ``(retval, stdout, stderr)``. +``retval`` is an integer representing a libc error code (e.g. EINVAL, +EPERM, or 0 for no error), ``stdout`` is a string containing any +non-error output, and ``stderr`` is a string containing any progress or +error explanation output. Either or both of the two strings may be empty. + +Implement the ``handle_command`` function to respond to the commands +when they are sent: + + +.. py:currentmodule:: mgr_module +.. automethod:: MgrModule.handle_command + + +Responses and Formatting +~~~~~~~~~~~~~~~~~~~~~~~~ + +Functions that handle manager commands are expected to return a three element +tuple with the type signature ``Tuple[int, str, str]``. The first element is a +return value/error code, where zero indicates no error and a negative `errno`_ +is typically used for error conditions. The second element corresponds to the +command's "output". The third element corresponds to the command's "error +output" (akin to stderr) and is frequently used to report textual error details +when the return code is non-zero. The ``mgr_module.HandleCommandResult`` type +can also be used in lieu of a response tuple. + +.. _`errno`: https://man7.org/linux/man-pages/man3/errno.3.html + +When the implementation of a command raises an exception one of two possible +approaches to handling the exception exist. First, the command function can do +nothing and let the exception bubble up to the manager. When this happens the +manager will automatically set a return code to -EINVAL and record a trace-back +in the error output. This trace-back can be very long in some cases. The second +approach is to handle an exception within a try-except block and convert the +exception to an error code that better fits the exception (converting a +KeyError to -ENOENT, for example). In this case the error output may also be +set to something more specific and actionable by the one calling the command. + +In many cases, especially in more recent versions of Ceph, manager commands are +designed to return structured output to the caller. Structured output includes +machine-parsable data such as JSON, YAML, XML, etc. JSON is the most common +structured output format returned by manager commands. As of Ceph Reef, there +are a number of new decorators available from the ``object_format`` module that +help manage formatting output and handling exceptions automatically. The +intent is that most of the implementation of a manager command can be written in +an idiomatic (aka "Pythonic") style and the decorators will take care of most of +the work needed to format the output and return manager response tuples. + +In most cases, net new code should use the ``Responder`` decorator. Example: + +.. code:: python + + @CLICommand('antigravity list wormholes', perm='r') + @Responder() + def list_wormholes(self, oid: str, details: bool = False) -> List[Dict[str, Any]]: + '''List wormholes associated with the supplied oid. + ''' + with self.open_wormhole_db() as db: + wormholes = db.query(oid=oid) + if not details: + return [{'name': wh.name} for wh in wormholes] + return [{'name': wh.name, 'age': wh.get_age(), 'destination': wh.dest} + for wh in wormholes] + +Formatting +++++++++++ + +The ``Responder`` decorator automatically takes care of converting Python +objects into a response tuple with formatted output. By default, this decorator +can automatically return JSON and YAML. When invoked from the command line the +``--format`` flag can be used to select the response format. If left +unspecified, JSON will be returned. The automatic formatting can be applied to +any basic Python type: lists, dicts, str, int, etc. Other objects can be +formatted automatically if they meet the ``SimpleDataProvider`` protocol - they +provide a ``to_simplified`` method. The ``to_simplified`` function must return +a simplified representation of the object made out of basic types. + +.. code:: python + + class MyCleverObject: + def to_simplified(self) -> Dict[str, int]: + # returns a python object(s) made up from basic types + return {"gravitons": 999, "tachyons": 404} + + @CLICommand('antigravity list wormholes', perm='r') + @Responder() + def list_wormholes(self, oid: str, details: bool = False) -> MyCleverObject: + '''List wormholes associated with the supplied oid. + ''' + ... + +The behavior of the automatic output formatting can be customized and extednted +to other types of formatting (XML, Plain Text, etc). As this is a complex +topic, please refer to the module documentation for the ``object_format`` +module. + + + +Error Handling +++++++++++++++ + +Additionally, the ``Responder`` decorator can automatically handle converting +some exceptions into response tuples. Any raised exception inheriting from +``ErrorResponseBase`` will be automatically converted into a response tuple. +The common approach will be to use ``ErrorResponse``, an exception type that +can be used directly and has arguments for the error output and return value or +it can be constructed from an existing exception using the ``wrap`` +classmethod. The wrap classmethod will automatically use the exception text and +if available the ``errno`` property of other exceptions. + +Converting our previous example to use this exception handling approach: + +.. code:: python + + @CLICommand('antigravity list wormholes', perm='r') + @Responder() + def list_wormholes(self, oid: str, details: bool = False) -> List[Dict[str, Any]]: + '''List wormholes associated with the supplied oid. + ''' + try: + with self.open_wormhole_db() as db: + wormholes = db.query(oid=oid) + except UnknownOIDError: + raise ErrorResponse(f"Unknown oid: {oid}", return_value=-errno.ENOENT) + except WormholeDBError as err: + raise ErrorResponse.wrap(err) + if not details: + return [{'name': wh.name} for wh in wormholes] + return [{'name': wh.name, 'age': wh.get_age(), 'destination': wh.dest} + for wh in wormholes] + + +.. note:: Because the decorator can not determine the difference between a + programming mistake and an expected error condition it does not try to + catch all exceptions. + + + +Additional Decorators ++++++++++++++++++++++ + +The ``object_format`` module provides additional decorators to complement +``Responder`` but for cases where ``Responder`` is insufficient or too "heavy +weight". + +The ``ErrorResponseHandler`` decorator exists for cases where you *must* still +return a manager response tuple but want to handle errors as exceptions (as in +typical Python code). In short, it works like ``Responder`` but only with +regards to exceptions. Just like ``Responder`` it handles exceptions that +inherit from ``ErrorResponseBase``. This can be useful in cases where you need +to return raw data in the output. Example: + +.. code:: python + + @CLICommand('antigravity dump config', perm='r') + @ErrorResponseHandler() + def dump_config(self, oid: str) -> Tuple[int, str, str]: + '''Dump configuration + ''' + # we have no control over what data is inside the blob! + try: + blob = self.fetch_raw_config_blob(oid) + return 0, blob, '' + except KeyError: + raise ErrorResponse("Blob does not exist", return_value=-errno.ENOENT) + + +The ``EmptyResponder`` decorator exists for cases where, on a success +condition, no output should be generated at all. If you used ``Responder`` and +default JSON formatting you may always see outputs like ``{}`` or ``[]`` if the +command completes without error. Instead, ``EmptyResponder`` helps you create +manager commands that obey the `Rule of Silence`_ when the command has no +interesting output to emit on success. The functions that ``EmptyResponder`` +decorate should always return ``None``. Like both ``Responder`` and +``ErrorResponseHandler`` exceptions that inhert from ``ErrorResponseBase`` will +be automatically processed. Example: + +.. code:: python + + @CLICommand('antigravity create wormhole', perm='rw') + @EmptyResponder() + def create_wormhole(self, oid: str, name: str) -> None: + '''Create a new wormhole. + ''' + try: + with self.open_wormhole_db() as db: + wh = Wormhole(name) + db.insert(oid=oid, wormhole=wh) + except UnknownOIDError: + raise ErrorResponse(f"Unknown oid: {oid}", return_value=-errno.ENOENT) + except InvalidWormholeError as err: + raise ErrorResponse.wrap(err) + except WormholeDBError as err: + raise ErrorResponse.wrap(err) + + +.. _`Rule of Silence`: http://www.linfo.org/rule_of_silence.html + + +Configuration options +--------------------- + +Modules can load and store configuration options using the +``set_module_option`` and ``get_module_option`` methods. + +.. note:: Use ``set_module_option`` and ``get_module_option`` to + manage user-visible configuration options that are not blobs (like + certificates). If you want to persist module-internal data or + binary configuration data consider using the `KV store`_. + +You must declare your available configuration options in the +``MODULE_OPTIONS`` class attribute, like this: + +.. code-block:: python + + MODULE_OPTIONS = [ + Option(name="my_option") + ] + +If you try to use set_module_option or get_module_option on options not declared +in ``MODULE_OPTIONS``, an exception will be raised. + +You may choose to provide setter commands in your module to perform +high level validation. Users can also modify configuration using +the normal `ceph config set` command, where the configuration options +for a mgr module are named like `mgr//