So, the scenario is I have producers and consumers in ratio 7:1, and I want to have a consistent and deterministic multilple mapping b/w the producers and consumers in my service. List of consumers is provided in the config to each of the producer, which is done via ansible. So, I try to implement the mapping logic in the ansible itself, rather than passing the entire list of consumers, and doing it inside producer service. So, I thought of using a custom filter to filter out from the list of consumers, and assign it to producer. Below is the custom filter I wrote:
#!/usr/bin/python
class FilterModule(object):
def filters(self):
return { 'map_producer_to_consumer': self.map_producer_to_consumer }
# consumer_servers: complete list of consumers servers
# producer_id: provided to each producer for mapping purpose
# producer_count: total no. of producers
# map_consumer_count: no. of consumers need to be mapped to each producer
# consumer_count: total no. of consumers
def map_producer_to_consumer(self, consumer_servers, producer_id, producer_count, map_consumer_count):
consumer_count = len(consumer_servers)
index_offset = 0 if producer_count%consumer_count else 1
rotation_count = (producer_id/consumer_count) % (map_consumer_count-1) # used for left rotation of mapped servers
map_consumer_indexes = [ (producer_count*i + producer_id + index_offset*i) % consumer_count for i in xrange(map_consumer_count)]
mapped_consumer_servers = [consumer_servers[map_consumer_indexes[0]]]
for i in xrange(1, map_consumer_count):
index = (i + rotation_count) % map_consumer_count
if i + rotation_count >= map_consumer_count:
mapped_consumer_servers.append( consumer_servers[map_consumer_indexes[index] + 1] )
else:
mapped_consumer_servers.append( consumer_servers[map_consumer_indexes[index]] )
return (',').join(mapped_consumer_servers)
This filter is working as expected, when using with static arguements like this:
"{{ tsdb_boxes | map_producer_to_consumer(2,3,3) }}"
but I want to make it use dynamic arguments via jinja2 templating, something like:
"{{ groups['producers'] | map_producer_to_consumer ({{ consumer_servers }}, {{ producer_id }}, {{ producer_count }}, {{ map_consumer_count }}) }}"
but its resulting in errors due to nesting of variables, which is not allowed in Jinja2. If I try something like this:
"{{ groups['producers'] }} | map_producer_to_consumer ({{ consumer_servers }}, {{ producer_id }}, {{ producer_count }}, {{ map_consumer_count }})"
it results in printing out the string like this:
['ip-1', 'ip-2'...] | map_producer_to_consumer (1000, 10, 150, 3)
Can someone please suggest what should be the best ansible way to achieve this. Should I use script module and convert the logic in bash, or it will be better to keep this inside the service only.
