Returners

By default the return values of the commands sent to the Salt minions are returned to the Salt master, however anything at all can be done with the results data.

By using a Salt returner, results data can be redirected to external data-stores for analysis and archival.

Returners pull their configuration values from the Salt minions. Returners are only configured once, which is generally at load time.

The returner interface allows the return data to be sent to any system that can receive data. This means that return data can be sent to a Redis server, a MongoDB server, a MySQL server, or any system.

Using Returners

All Salt commands will return the command data back to the master. Specifying returners will ensure that the data is _also_ sent to the specified returner interfaces.

Specifying what returners to use is done when the command is invoked:

salt '*' test.ping --return redis_return

This command will ensure that the redis_return returner is used.

It is also possible to specify multiple returners:

salt '*' test.ping --return mongo_return,redis_return,cassandra_return

In this scenario all three returners will be called and the data from the test.ping command will be sent out to the three named returners.

Writing a Returner

A returner is a Python module containing at minimum a returner function. Other optional functions can be included to add support for master_job_cache, external_job_cache, and Event Returners.

returner
The returner function must accept a single argument. The argument contains return data from the called minion function. If the minion function test.ping is called, the value of the argument will be a dictionary. Run the following command from a Salt master to get a sample of the dictionary:
salt-call --local --metadata test.ping --out=pprint
import redis
import json

def returner(ret):
    '''
    Return information to a redis server
    '''
    # Get a redis connection
    serv = redis.Redis(
                host='redis-serv.example.com',
                port=6379,
                db='0')
    serv.sadd("%(id)s:jobs" % ret, ret['jid'])
    serv.set("%(jid)s:%(id)s" % ret, json.dumps(ret['return']))
    serv.sadd('jobs', ret['jid'])
    serv.sadd(ret['jid'], ret['id'])

The above example of a returner set to send the data to a Redis server serializes the data as JSON and sets it in redis.

Master Job Cache Support

master_job_cache, external_job_cache, and Event Returners. Salt's master_job_cache allows returners to be used as a pluggable replacement for the Default Job Cache. In order to do so, a returner must implement the following functions:

Note

The code samples contained in this section were taken from the cassandra_cql returner.

prep_jid

Ensures that job ids (jid) don't collide, unless passed_jid is provided.

nochache is an optional boolean that indicates if return data should be cached. passed_jid is a caller provided jid which should be returned unconditionally.

def prep_jid(nocache, passed_jid=None):  # pylint: disable=unused-argument
    '''
    Do any work necessary to prepare a JID, including sending a custom id
    '''
    return passed_jid if passed_jid is not None else salt.utils.jid.gen_jid()
save_load
Save job information. The jid is generated by prep_jid and should be considered a unique identifier for the job. The jid, for example, could be used as the primary/unique key in a database. The load is what is returned to a Salt master by a minion. The following code example stores the load as a JSON string in the salt.jids table.
def save_load(jid, load):
    '''
    Save the load to the specified jid id
    '''
    query = '''INSERT INTO salt.jids (
                 jid, load
               ) VALUES (
                 '{0}', '{1}'
               );'''.format(jid, json.dumps(load))

    # cassandra_cql.cql_query may raise a CommandExecutionError
    try:
        __salt__['cassandra_cql.cql_query'](query)
    except CommandExecutionError:
        log.critical('Could not save load in jids table.')
        raise
    except Exception as e:
        log.critical('''Unexpected error while inserting into
         jids: {0}'''.format(str(e)))
        raise
get_load
must accept a job id (jid) and return the job load stored by save_load, or an empty dictionary when not found.
def get_load(jid):
    '''
    Return the load data that marks a specified jid
    '''
    query = '''SELECT load FROM salt.jids WHERE jid = '{0}';'''.format(jid)

    ret = {}

    # cassandra_cql.cql_query may raise a CommandExecutionError
    try:
        data = __salt__['cassandra_cql.cql_query'](query)
        if data:
            load = data[0].get('load')
            if load:
                ret = json.loads(load)
    except CommandExecutionError:
        log.critical('Could not get load from jids table.')
        raise
    except Exception as e:
        log.critical('''Unexpected error while getting load from
         jids: {0}'''.format(str(e)))
        raise

    return ret

External Job Cache Support

Salt's external_job_cache extends the master_job_cache. External Job Cache support requires the following functions in addition to what is required for Master Job Cache support:

get_jid
Return a dictionary containing the information (load) returned by each minion when the specified job id was executed.

Sample:

{
    "local": {
        "master_minion": {
            "fun_args": [],
            "jid": "20150330121011408195",
            "return": true,
            "retcode": 0,
            "success": true,
            "cmd": "_return",
            "_stamp": "2015-03-30T12:10:12.708663",
            "fun": "test.ping",
            "id": "master_minion"
        }
    }
}
get_fun
Return a dictionary of minions that called a given Salt function as their last function call.

Sample:

{
    "local": {
        "minion1": "test.ping",
        "minion3": "test.ping",
        "minion2": "test.ping"
    }
}
get_jids
Return a list of all job ids.

Sample:

{
    "local": [
        "20150330121011408195",
        "20150330195922139916"
    ]
}
get_minions
Returns a list of minions

Sample:

{
     "local": [
         "minion3",
         "minion2",
         "minion1",
         "master_minion"
     ]
}

Please refer to one or more of the existing returners (i.e. mysql, cassandra_cql) if you need further clarification.

Event Support

An event_return function must be added to the returner module to allow events to be logged from a master via the returner. A list of events are passed to the function by the master.

The following example was taken from the MySQL returner. In this example, each event is inserted into the salt_events table keyed on the event tag. The tag contains the jid and therefore is guaranteed to be unique.

def event_return(events):
 '''
 Return event to mysql server

 Requires that configuration be enabled via 'event_return'
 option in master config.
 '''
 with _get_serv(events, commit=True) as cur:
     for event in events:
         tag = event.get('tag', '')
         data = event.get('data', '')
         sql = '''INSERT INTO `salt_events` (`tag`, `data`, `master_id` )
                  VALUES (%s, %s, %s)'''
         cur.execute(sql, (tag, json.dumps(data), __opts__['id']))

Custom Returners

Place custom returners in a _returners directory within the file_roots specified by the master config file.

Custom returners are distributed when any of the following are called:

Any custom returners which have been synced to a minion that are named the same as one of Salt's default set of returners will take the place of the default returner with the same name.

Naming the Returner

Note that a returner's default name is its filename (i.e. foo.py becomes returner foo), but that its name can be overridden by using a __virtual__ function. A good example of this can be found in the redis returner, which is named redis_return.py but is loaded as simply redis:

try:
    import redis
    HAS_REDIS = True
except ImportError:
    HAS_REDIS = False

__virtualname__ = 'redis'

def __virtual__():
    if not HAS_REDIS:
        return False
    return __virtualname__

Testing the Returner

The returner, prep_jid, save_load, get_load, and event_return functions can be tested by configuring the master_job_cache and Event Returners in the master config file and submitting a job to test.ping each minion from the master.

Once you have successfully exercised the Master Job Cache functions, test the External Job Cache functions using the ret execution module.

salt-call ret.get_jids cassandra_cql --output=json
salt-call ret.get_fun cassandra_cql test.ping --output=json
salt-call ret.get_minions cassandra_cql --output=json
salt-call ret.get_jid cassandra_cql 20150330121011408195 --output=json

Event Returners

For maximum visibility into the history of events across a Salt infrastructure, all events seen by a salt master may be logged to one or more returners.

To enable event logging, set the event_return configuration option in the master config to the returner(s) which should be designated as the handler for event returns.

Note

Not all returners support event returns. Verify a returner has an event_return() function before using.

Note

On larger installations, many hundreds of events may be generated on a busy master every second. Be certain to closely monitor the storage of a given returner as Salt can easily overwhelm an underpowered server with thousands of returns.