[zmq] Update configurations documentation
In this change new configurations appeared in Ocata release like dynamic connections and other types of proxied deployments being described. Change-Id: Id6e9b062101d8916323edc143ea5379585192581
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@ -36,7 +36,7 @@ Currently, ZeroMQ is one of the RPC backend drivers in oslo.messaging. ZeroMQ
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can be the only RPC driver across the OpenStack cluster.
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This document provides deployment information for this driver in oslo_messaging.
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Other than AMQP-based drivers, like RabbitMQ, ZeroMQ doesn't have
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Other than AMQP-based drivers, like RabbitMQ, default ZeroMQ doesn't have
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any central brokers in oslo.messaging, instead, each host (running OpenStack
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services) is both ZeroMQ client and server. As a result, each host needs to
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listen to a certain TCP port for incoming connections and directly connect
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@ -78,15 +78,16 @@ Assuming the following systems as a goal.
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| Horizon |
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+---------------------+
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=============
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Configuration
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=============
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===================
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Basic Configuration
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===================
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Enabling (mandatory)
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--------------------
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To enable the driver the 'transport_url' option must be set to 'zmq://'
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in the section [DEFAULT] of the conf file, the 'rpc_zmq_host' flag
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in the section [DEFAULT] of the conf file, the 'rpc_zmq_host' option
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must be set to the hostname of the current node. ::
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[DEFAULT]
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@ -95,15 +96,23 @@ must be set to the hostname of the current node. ::
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[oslo_messaging_zmq]
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rpc_zmq_host = {hostname}
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Default configuration of zmq driver is called 'Static Direct Connections' (To
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learn more about zmq driver configurations please proceed to the corresponding
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section 'Existing Configurations'). That means that all services connect
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directly to each other and all connections are static so we open them at the
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beginning of service's lifecycle and close them only when service quits. This
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configuration is the simplest one since it doesn't require any helper services
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(proxies) other than matchmaker to be running.
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Match Making (mandatory)
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------------------------
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Matchmaking (mandatory)
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-----------------------
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The ZeroMQ driver implements a matching capability to discover hosts available
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for communication when sending to a bare topic. This allows broker-less
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communications.
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The MatchMaker is pluggable and it provides two different MatchMaker classes.
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The Matchmaker is pluggable and it provides two different Matchmaker classes.
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MatchmakerDummy: default matchmaker driver for all-in-one scenario (messages
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are sent to itself; used mainly for testing).
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@ -120,14 +129,24 @@ specify the URL as follows::
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In order to cleanup redis storage from expired records (e.g. target listener
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goes down) TTL may be applied for keys. Configure 'zmq_target_expire' option
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which is 120 (seconds) by default. The option is related not specifically to
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which is 300 (seconds) by default. The option is related not specifically to
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redis so it is also defined in [oslo_messaging_zmq] section. If option value
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is <= 0 then keys don't expire and live forever in the storage.
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MatchMaker Data Source (mandatory)
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The other option is 'zmq_target_update' (180 seconds by default) which
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specifies how often each RPC-Server should update the matchmaker. This option's
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optimal value generally is zmq_target_expire / 2 (or 1.5). It is recommended to
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calculate it based on 'zmq_target_expire' so services records wouldn't expire
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earlier than being updated from alive services.
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Generally matchmaker can be considered as an alternate approach to services
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heartbeating.
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Matchmaker Data Source (mandatory)
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----------------------------------
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MatchMaker data source is stored in files or Redis server discussed in the
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Matchmaker data source is stored in files or Redis server discussed in the
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previous section. How to make up the database is the key issue for making ZeroMQ
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driver work.
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@ -154,63 +173,7 @@ To deploy redis with HA follow the `sentinel-install`_ instructions. From the
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messaging driver's side you will need to setup following configuration ::
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[DEFAULT]
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transport_url = "zmq+redis://host1:26379,host2:26379,host3:26379"
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Restrict the number of TCP sockets on controller
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------------------------------------------------
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The most heavily used RPC pattern (CALL) may consume too many TCP sockets on
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controller node in directly connected configuration. To solve the issue
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ROUTER proxy may be used.
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In order to configure driver to use ROUTER proxy set up the 'use_router_proxy'
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option to true in [oslo_messaging_zmq] section (false is set by default).
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For example::
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use_router_proxy = true
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Not less than 3 proxies should be running on controllers or on stand alone
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nodes. The parameters for the script oslo-messaging-zmq-proxy should be::
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oslo-messaging-zmq-proxy
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--config-file /etc/oslo/zeromq.conf
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--log-file /var/log/oslo/zeromq-router-proxy.log
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--host node-123
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--frontend-port 50001
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--backend-port 50002
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--publisher-port 50003
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--debug True
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Command line arguments like host, frontend_port, backend_port and publisher_port
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respectively can also be set in [zmq_proxy_opts] section of a configuration
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file (i.e., /etc/oslo/zeromq.conf). All arguments are optional.
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Port value of 0 means random port (see the next section for more details).
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Fanout-based patterns like CAST+Fanout and notifications always use proxy
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as they act over PUB/SUB, 'use_pub_sub' option defaults to true. In such case
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publisher proxy should be running. Actually proxy does both: routing to a
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DEALER endpoint for direct messages and publishing to all subscribers over
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zmq.PUB socket.
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If not using PUB/SUB (use_pub_sub = false) then fanout will be emulated over
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direct DEALER/ROUTER unicast which is possible but less efficient and therefore
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is not recommended. In a case of direct DEALER/ROUTER unicast proxy is not
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needed.
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This option can be set in [oslo_messaging_zmq] section.
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For example::
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use_pub_sub = true
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In case of using a proxy all publishers (clients) talk to servers over
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the proxy connecting to it via TCP.
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You can specify ZeroMQ options in /etc/oslo/zeromq.conf if necessary.
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transport_url = "zmq+sentinel://host1:26379,host2:26379,host3:26379"
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Listening Address (optional)
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@ -235,18 +198,379 @@ controls number of retries before 'ports range exceeded' failure.
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For example::
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rpc_zmq_min_port = 9050
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rpc_zmq_max_port = 10050
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rpc_zmq_min_port = 49153
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rpc_zmq_max_port = 65536
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rpc_zmq_bind_port_retries = 100
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=======================
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Existing Configurations
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=======================
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Static Direct Connections
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-------------------------
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The example of service config file::
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[DEFAULT]
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transport_url = "zmq+redis://host-1:6379"
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[oslo_messaging_zmq]
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use_pub_sub = false
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use_router_proxy = false
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use_dynamic_connections = false
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zmq_target_expire = 60
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zmq_target_update = 30
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rpc_zmq_min_port = 49153
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rpc_zmq_max_port = 65536
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In both static and dynamic direct connections configuration it is necessary to
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configure firewall to open binding port range on each node::
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iptables -A INPUT -p tcp --match multiport --dports 49152:65535 -j ACCEPT
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The sequrity recommendation here (it is general for any RPC backend) is to
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setup private network for message bus and another open network for public APIs.
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ZeroMQ driver doesn't support authentication and encryption on its level.
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As stated above this configuration is the simplest one since it requires only a
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Matchmaker service to be running. That is why driver's options configured by
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default in a way to use this type of topology.
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The biggest advantage of static direct connections (other than simplicity) is
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it's huge performance. On small deployments (20 - 50 nodes) it can outperform
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brokered solutions (or solutions with proxies) 3x - 5x times. It becomes possible
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because this configuration doesn't have a central node bottleneck so it's
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throughput is limited by only a TCP and network bandwidth.
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Unfortunately this approach can not be applied as is on a big scale (over 500 nodes).
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The main problem is the number of connections between services and particularly
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the number of connections on each controller node grows (in a worst case) as
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a square function of number of the whole running services. That's not
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appropriate.
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However this approach can be successfully used and is recommended to be used
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when services on controllers doesn't talk to agent services on resource nodes
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using oslo.messaging RPC, but RPC is used only to communicate controller
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services between each other.
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Examples here may be Cinder+Ceph backend and Ironic how it utilises
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oslo.messaging.
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For all the other cases like Nova and Neutron on a big scale using proxy-based
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configurations or dynamic connections configuration is more appropriate.
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The exception here may be the case when using OpenStack services inside Docker
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containers with Kubernetes. Since Kubernetes already solves similar problems by
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using KubeProxy and virtual IP addresses for each container. So it manages all
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the traffic using iptables which is more than appropriate to solve the problem
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described above.
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Summing up it is recommended to use this type of zmq configuration for
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1. Small clouds (up to 100 nodes)
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2. Cinder+Ceph deployment
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3. Ironic deployment
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4. OpenStack + Kubernetes (OpenStack in containers) deployment
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Dynamic Direct Connections
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--------------------------
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The example of service config file::
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[DEFAULT]
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transport_url = "zmq+redis://host-1:6379"
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[oslo_messaging_zmq]
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use_pub_sub = false
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use_router_proxy = false
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use_dynamic_connections = true
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zmq_failover_connections = 2
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zmq_linger = 60
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zmq_target_expire = 60
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zmq_target_update = 30
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rpc_zmq_min_port = 49153
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rpc_zmq_max_port = 65536
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The 'use_dynamic_connections = true' obviously states that connections are dynamic.
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'zmq_linger' become crucial with dynamic connections in order to avoid socket
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leaks. If socket being connected to a wrong (dead) host which somehow still
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present in the Matchmaker and message was sent, then the socket can not be closed
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until message stays in the queue (the default linger is infinite waiting). So
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need to specify linger explicitly.
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Services often run more than one worker on the same topic. Workers are equal, so
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any can handle the message. In order to connect to more than one available worker
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need to setup 'zmq_failover_connections' option to some value (2 by default which
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means 2 additional connections). Take care because it may also result in slow-down.
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All recommendations regarding port ranges described in previous section are also
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valid here.
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Most things are similar to what we had with static connections the only
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difference is that each message causes connection setup and disconnect afterwards
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immediately after message was sent.
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The advantage of this deployment is that average number of connections on
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controller node at any moment is not high even for quite large deployments.
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The disadvantage is overhead caused by need to connect/disconnect per message.
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So this configuration can with no doubt be considered as the slowest one. The
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good news is the RPC of OpenStack doesn't require "thousands message per second"
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bandwidth per each particular service (do not confuse with central broker/proxy
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bandwidth which is needed as high as possible for a big scale and can be a
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serious bottleneck).
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One more bad thing about this particular configuration is fanout. Here it is
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completely linear complexity operation and it suffers the most from
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connect/disconnect overhead per message. So for fanout it is fair to say that
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services can have significant slow-down with dynamic connections.
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The recommended way to solve this problem is to use combined solution with
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proxied PUB/SUB infrastructure for fanout and dynamic direct connections for
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direct message types (plain CAST and CALL messages). This combined approach
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will be described later in the text.
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Router Proxy
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------------
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The example of service config file::
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[DEFAULT]
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transport_url = "zmq+redis://host-1:6379"
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[oslo_messaging_zmq]
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use_pub_sub = false
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use_router_proxy = true
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use_dynamic_connections = false
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The example of proxy config file::
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[DEFAULT]
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transport_url = "zmq+redis://host-1:6379"
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[oslo_messaging_zmq]
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use_pub_sub = false
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[zmq_proxy_opt]
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host = host-1
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RPC may consume too many TCP sockets on controller node in directly connected
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configuration. To solve the issue ROUTER proxy may be used.
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In order to configure driver to use ROUTER proxy set up the 'use_router_proxy'
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option to true in [oslo_messaging_zmq] section (false is set by default).
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Pay attention to 'use_pub_sub = false' line, which has to match for all
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services and proxies configs, so it wouldn't work if proxy uses PUB/SUB and
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services don't.
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Not less than 3 proxies should be running on controllers or on stand alone
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nodes. The parameters for the script oslo-messaging-zmq-proxy should be::
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oslo-messaging-zmq-proxy
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--config-file /etc/oslo/zeromq.conf
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--log-file /var/log/oslo/zeromq-router-proxy.log
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--host node-123
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--frontend-port 50001
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--backend-port 50002
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--debug
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Config file for proxy consists of default section, 'oslo_messaging_zmq' section
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and additional 'zmq_proxy_opts' section.
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Command line arguments like host, frontend_port, backend_port and publisher_port
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respectively can also be set in 'zmq_proxy_opts' section of a configuration
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file (i.e., /etc/oslo/zeromq.conf). All arguments are optional.
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Port value of 0 means random port (see the next section for more details).
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Take into account that --debug flag makes proxy to make a log record per every
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dispatched message which influences proxy performance significantly. So it is
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not recommended flag to use in production. Without --debug there will be only
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Matchmaker updates or critical errors in proxy logs.
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In this configuration we use proxy as a very simple dispatcher (so it has the
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best performance with minimal overhead). The only thing proxy does is getting
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binary routing-key frame from the message and dispatch message on this key.
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In this kind of deployment client is in charge of doing fanout. Before sending
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fanout message client takes a list of available hosts for the topic and sends
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as many messages as the number of hosts it got.
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This configuration just uses DEALER/ROUTER pattern of ZeroMQ and doesn't use
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PUB/SUB as it was stated above.
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Disadvantage of this approach is again slower client fanout. But it is much
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better than with dynamic direct connections because we don't need to connect
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and disconnect per each message.
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ZeroMQ PUB/SUB Infrastructure
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-----------------------------
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The example of service config file::
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[DEFAULT]
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transport_url = "zmq+redis://host-1:6379"
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[oslo_messaging_zmq]
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use_pub_sub = true
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use_router_proxy = true
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use_dynamic_connections = false
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The example of proxy config file::
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[DEFAULT]
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transport_url = "zmq+redis://host-1:6379"
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[oslo_messaging_zmq]
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use_pub_sub = true
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[zmq_proxy_opt]
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host = host-1
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It seems obvious that fanout pattern of oslo.messaging maps on ZeroMQ PUB/SUB
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pattern, but it is only at first glance. It does really, but lets look a bit
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closer.
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First caveat is that in oslo.messaging it is a client who makes fanout (and
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generally initiates conversation), server is passive. While in ZeroMQ publisher
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is a server and subscribers are clients. And here is the problem: RPC-servers
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are subscribers in terms of ZeroMQ PUB/SUB, they hold the SUB socket and wait
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for messages. And they don't know anything about RPC-clients, and clients
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generally come later than servers. So servers don't have a PUB to subscribe
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on start, so we need to introduce something in the middle, and here the proxy
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plays the role.
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Publisher proxy has ROUTER socket on the front-end and PUB socket on the back-end.
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So client connects to ROUTER and sends a single message to a publisher proxy.
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Proxy redirects this message to PUB socket which performs actual publishing.
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Command to run central publisher proxy::
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oslo-messaging-zmq-proxy
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--config-file /etc/oslo/zeromq.conf
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--log-file /var/log/oslo/zeromq-router-proxy.log
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--host node-123
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--frontend-port 50001
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--publisher-port 50003
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--debug
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When we run a publisher proxy we need to specify a --publisher-port option.
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Random port will be picked up otherwise and clients will get it from the
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Matchmaker.
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The advantage of this approach is really fast fanout, while it takes time on
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proxy to publish, but ZeroMQ PUB/SUB is one of the fastest fanout pattern
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implementations. It also makes clients faster, because they need to send only a
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single message to a proxy.
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In order to balance load and HA it is recommended to have at least 3 proxies basically,
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but the number of running proxies is not limited. They also don't form a cluster,
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so there are no limitations on number caused by consistency algorithm requirements.
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The disadvantage is that number of connections on proxy increased twice compared
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to previous deployment, because we still need to use router for direct messages.
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The documented limitation of ZeroMQ PUB/SUB is 10k subscribers.
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In order to limit the number of subscribers and connections the local proxies
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may be used. In order to run local publisher the following command may be used::
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oslo-messaging-zmq-proxy
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--local-publisher
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--config-file /etc/oslo/zeromq.conf
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--log-file /var/log/oslo/zeromq-router-proxy.log
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--host localhost
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--publisher-port 60001
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--debug
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Pay attention to --local-publisher flag which specifies the type of a proxy.
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Local publishers may be running on every single node of a deployment. To make
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services use of local publishers the 'subscribe_on' option has to be specified
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in service's config file::
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[DEFAULT]
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transport_url = "zmq+redis://host-1:6379"
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[oslo_messaging_zmq]
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use_pub_sub = true
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use_router_proxy = true
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use_dynamic_connections = false
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subscribe_on = localhost:60001
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If we forgot to specify the 'subscribe_on' services will take info from Matchmaker
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and still connect to a central proxy, so the trick wouldn't work. Local proxy
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||||
gets all the needed info from the matchmaker in order to find central proxies
|
||||
and subscribes on them. Frankly speaking you can pub a central proxy in the
|
||||
'subscribe_on' value, even a list of hosts may be passed the same way as we do
|
||||
for the transport_url::
|
||||
|
||||
subscribe_on = host-1:50003,host-2:50003,host-3:50003
|
||||
|
||||
This is completely valid, just not necessary because we have information about
|
||||
central proxies in Matchmaker. One more thing to highlight about 'subscribe_on'
|
||||
is that it has higher priority than Matchmaker if being explicitly mentioned.
|
||||
|
||||
Concluding all the above, fanout over PUB/SUB proxies is the best choice
|
||||
because of static connections infrastructure, fail over when one or some publishers
|
||||
die, and ZeroMQ PUB/SUB high performance.
|
||||
|
||||
|
||||
What If Mix Different Configurations?
|
||||
-------------------------------------
|
||||
|
||||
Three boolean variables 'use_pub_sub', 'use_router_proxy' and 'use_dynamic_connections'
|
||||
give us exactly 8 possible combinations. But from practical perspective not all
|
||||
of them are usable. So lets discuss only those which make sense.
|
||||
|
||||
The main recommended combination is Dynamic Direct Connections plus PUB/SUB
|
||||
infrastructure. So we deploy PUB/SUB proxies as described in corresponding
|
||||
paragraph (either with local+central proxies or with only a central proxies).
|
||||
And the services configuration file will look like the following::
|
||||
|
||||
[DEFAULT]
|
||||
transport_url = "zmq+redis://host-1:6379"
|
||||
|
||||
[oslo_messaging_zmq]
|
||||
use_pub_sub = true
|
||||
use_router_proxy = false
|
||||
use_dynamic_connections = true
|
||||
|
||||
So we just tell the driver not to pass direct messages CALL and CAST over router,
|
||||
but send them directly to RPC servers. All the details of configuring services
|
||||
and port ranges has to be taken from 'Dynamic Direct Connections' paragraph.
|
||||
So it's combined configuration. Currently it is the best choice from number of
|
||||
connections perspective.
|
||||
|
||||
Frankly speaking, deployment from the 'ZeroMQ PUB/SUB Infrastructure' section is
|
||||
also a combination of 'Router Proxy' with PUB/SUB, we've just used the same
|
||||
proxies for both.
|
||||
|
||||
Here we've discussed combination inside the same service. But configurations can
|
||||
also be combined on a higher level, a level of services. So you could have for
|
||||
example a deployment where Cinder uses static direct connections and Nova/Neutron
|
||||
use combined PUB/SUB + dynamic direct connections. But such approach needs additional
|
||||
caution and may be confusing for cloud operators. Still it provides maximum
|
||||
optimization of performance and number of connections on proxies and controller
|
||||
nodes.
|
||||
|
||||
|
||||
================
|
||||
DevStack Support
|
||||
----------------
|
||||
================
|
||||
|
||||
ZeroMQ driver has been supported by DevStack. The configuration is as follows::
|
||||
|
||||
ENABLED_SERVICES+=,-rabbit,zeromq
|
||||
ZEROMQ_MATCHMAKER=redis
|
||||
ZeroMQ driver can be tested on a single node deployment with DevStack. Take
|
||||
into account that on a single node it is not that obvious any performance
|
||||
increase compared to other backends. To see significant speed up you need at least
|
||||
20 nodes.
|
||||
|
||||
In local.conf [localrc] section need to enable zmq plugin which lives in
|
||||
`devstack-plugin-zmq`_ repository.
|
||||
|
||||
Loading…
Reference in New Issue
Block a user