def azs_lookup(bosslet_config, compatibility=None):
    """Lookup all of the Availablity Zones for the connected region.

    Args:
        bosslet_config (BossConfiguration) : Bosslet configuration
        compatiblity (str|None) : AVAILABILITY_ZONE_USAGE key to apply
    Returns:
        (list) : List of tuples (availability zone, zone letter)
    """
    client = bosslet_config.session.client('ec2')
    response = client.describe_availability_zones()

    rtn = [(z["ZoneName"], z["ZoneName"][-1]) for z in response["AvailabilityZones"]]

    if compatibility:
        try:
            limits = bosslet_config.AVAILABILITY_ZONE_USAGE[compatibility]
        except:
            pass # Don't do anything
        else:
            for az in rtn.copy():
                if az[1] not in limits:
                    rtn.remove(az)

    return rtn