编者按：本文介绍的是如何在RYU上通过使用select group来实现multipath，从而实现流量的调度，完成简单的负载均衡Demo。在OpenFlow13中有group table,可用于实现组播和冗余容灾等功能。实验中还使用了OpenvSwitch的队列queue完成了对链路带宽的保障。
要完成多径传输，那么网络拓扑必然有loop，所以首先要解决由于loop而可能产生的storm，解决方案在《基于SDN的RYU应用开发之ARP代理》文中已经提出。
网络拓扑：
"""Custom loop topo example
There are two paths between host1 and host2.
|--------switch2 --------|
| |
host1 --- switch1 switch4 -----host2
| | |------host3
-------- switch3 ---------
|
host4
Adding the 'topos' dict with a key/value pair to generate our newly defined
topology enables one to pass in '--topo=mytopo' from the command line.
"""
from mininet.topo import Topo
class MyTopo(Topo):
"Simple loop topology example."
def __init__(self):
"Create custom loop topo."
# Initialize topology
Topo.__init__(self)
# Add hosts and switches
host1 = self.addHost('h1')
host2 = self.addHost('h2')
host3 = self.addHost('h3')
#host4 = self.addHost('h4')
switch1 = self.addSwitch("s1")
switch2 = self.addSwitch("s2")
switch3 = self.addSwitch("s3")
switch4 = self.addSwitch("s4")
# Add links
self.addLink(switch1, host1, 1)
self.addLink(switch1, switch2, 2, 1)
self.addLink(switch1, switch3, 3, 1)
self.addLink(switch2, switch4, 2, 1)
self.addLink(switch3, switch4, 2, 2)
self.addLink(switch4, host2, 3)
self.addLink(switch4, host3, 4)
#self.addLink(switch3, host4, 3)
topos = {'mytopo': (lambda: MyTopo())}
Multipath：
解决网络可能形成风暴的问题之后，可以使用select类型的group_table来实现多径功能。
def send_group_mod(self, datapath):
ofp = datapath.ofproto
ofp_parser = datapath.ofproto_parser
port_1 = 3
actions_1 = [ofp_parser.OFPActionOutput(port_1)]
port_2 = 2
actions_2 = [ofp_parser.OFPActionOutput(port_2)]
weight_1 = 50
weight_2 = 50
watch_port = ofproto_v1_3.OFPP_ANY
watch_group = ofproto_v1_3.OFPQ_ALL
buckets = [
ofp_parser.OFPBucket(weight_1, watch_port, watch_group, actions_1),
ofp_parser.OFPBucket(weight_2, watch_port, watch_group, actions_2)]
group_id = 50
req = ofp_parser.OFPGroupMod(
datapath, ofp.OFPFC_ADD,
ofp.OFPGT_SELECT, group_id, buckets)
datapath.send_msg(req)
不知道现在OVS的select的key是否已经改变，原先的key为dl_dst。匹配成功的flow，在执行select时，是以dl_dst为key,进行判断，从而从buckets中选择一个action_list。
查看组表信息：
sudo ovs-ofctl dump-groups s1 -O OpenFlow13
查看流表信息：
sudo ovs-ofctl dump-flows s1 -O OpenFlow13
QoS：
首先我们知道OpenFlow无法创建队列。所以我们可以通过ovsdb来配置队列，也可以直接使用ovs命令配置:
ovs-vsctl -- set Port s1-eth2 qos=@newqos \
-- --id=@newqos create QoS type=linux-htb other-config:max-rate=250000000 queues=0=@q0\
-- --id=@q0 create Queue other-config:min-rate=8000000 other-config:max-rate=150000000\
ovs-vsctl -- set Port s1-eth3 qos=@defaultqos\
-- --id=@defaultqos create QoS type=linux-htb other-config:max-rate=300000000 queues=1=@q1\
-- --id=@q1 create Queue other-config:min-rate=5000000 other-config:max-rate=200000000
ovs-vsctl list queue
以上代码在s1-eth2上创建了queue 0,在s1-eth3上创建了queue 0和queue 1。并配置了max_rate和min_rate。
查看queue的信息可以使用：
sudo ovs-ofctl queue-stats s1 2 -O OpenFlow13
列举port查看qos：
ovs-vsctl list port
列举queue：
ovs-vsctl list queue
删除QOS:
sudo ovs-vsctl --all destroy qos
sudo ovs-vsctl --all destroy queue
区别于OpenFlow1.0, OpenFlow1.3中的入队操作只有一个queue_id,需要额外指定port。即指定数据如某一个队列的话需要如下的actions:
actions_2 = [ofp_parser.OFPActionSetQueue(0), ofp_parser.OFPActionOutput(port_2)]
所以使用group的情况下，完成QoS功能函数如下：
def send_group_mod(self, datapath):
ofp = datapath.ofproto
ofp_parser = datapath.ofproto_parser
port_1 = 3
queue_1 = ofp_parser.OFPActionSetQueue(0)
actions_1 = [queue_1, ofp_parser.OFPActionOutput(port_1)]
port_2 = 2
queue_2 = ofp_parser.OFPActionSetQueue(0)
actions_2 = [queue_2, ofp_parser.OFPActionOutput(port_2)]
weight_1 = 50
weight_2 = 50
watch_port = ofproto_v1_3.OFPP_ANY
watch_group = ofproto_v1_3.OFPQ_ALL
buckets = [
ofp_parser.OFPBucket(weight_1, watch_port, watch_group, actions_1),
ofp_parser.OFPBucket(weight_2, watch_port, watch_group, actions_2)]
group_id = 50
req = ofp_parser.OFPGroupMod(
datapath, ofp.OFPFC_ADD,
ofp.OFPGT_SELECT, group_id, buckets)
datapath.send_msg(req)
负载均衡：
从图中我们可以看到，pingall连通性没有问题。第一个iperf是在没有设置队列的情况下，由于找不到队列，所以不如队，只转发，此时带宽为26.4Gbits/sec。之后的测试数据为设置队列之后的数据。可以看出h1到h2之间的带宽是300Mbits/sec，而h1到h3的带宽是150Mbits/sec。
原因在于我们将h1到h2的数据流在组表中选择了s1-eth3的queue 0，而该队列的最大带宽是300M。
同时另一个从h1到h3的数据流，在hash过程中，选择了s1-eth2端口的queue 0，该队列的最大速度为150M。
下图为queue information：
可以看到，port 2 queue 0和port 3 queue 0有数据，而port 3 queue 1没有数据：
上图为s1和s4的组表和流表信息，从s4的流表信息（后部分流表）可知，同样是s1到s4的数据，dl_dst为h2的数据从port 2进入，而dl_dst为h3的数据从port 1进入，验证了数据传输过程使用了多径传输，合理利用了带宽空间。多径传输可以充分利用链路带宽，提高链路利用率。同时这个实验简单粗暴地完成了两条链路的负载均衡（将不同的数据流平均地分摊到了两条path上，由于对不同Path限制了不同的带宽，所以，流量并不是平均的）。根据拓扑及流量情况，添加算法计算合理流量路径，可以完成更灵活有效的负载均衡功能。
后语
这其实是简单的实验，但是由于在安装OVS的过程中遇到了很多的问题，所以过程比较痛苦，写下来，以备不时之需，也有可能帮助到别人吧。提供一个纯从OVS上配置的方案，相比之下比开发控制要简单一些。之前的博文的名字是：Multipath and QoS Application on RYU,但是后来导师提醒Multipath和QoS不是一个层面的，才发现自己学识粗浅。需要努力的地方还太多。所以本篇博文被我生生改成Load balance的题目，虽然很牵强，但是相比之下，犯的错误更少一些。源码没有全部贴出来是因为我写的APP也可以出售的。后续应该会上传Github。详情可以邮件沟通。
折叠版代码如下：
# Author:muzixing
# Time:2014/10/19
#
from ryu.base import app_manager
from ryu.controller import ofp_event
from ryu.controller.handler import CONFIG_DISPATCHER
from ryu.controller.handler import MAIN_DISPATCHER, HANDSHAKE_DISPATCHER
from ryu.controller.handler import set_ev_cls
from ryu.ofproto import ofproto_v1_3
from ryu.lib.packet import packet
from ryu.lib.packet import ethernet
from ryu.lib.packet import arp
from ryu.lib.packet import ipv4
from ryu.lib.packet import icmp
from ryu import utils
from ryu.lib import addrconv
import struct
import socket
ETHERNET = ethernet.ethernet.__name__
ETHERNET_MULTICAST = "ff:ff:ff:ff:ff:ff"
ARP = arp.arp.__name__
ICMP = icmp.icmp.__name__
IPV4 = ipv4.ipv4.__name__
def ip2long(ip):
return struct.unpack("!I", socket.inet_aton(ip))[0]
class MULTIPATH_13(app_manager.RyuApp):
OFP_VERSIONS = [ofproto_v1_3.OFP_VERSION]
def __init__(self, *args, **kwargs):
super(MULTIPATH_13, self).__init__(*args, **kwargs)
self.mac_to_port = {}
self.arp_table = {}
self.sw = {}
@set_ev_cls(ofp_event.EventOFPSwitchFeatures, CONFIG_DISPATCHER)
def switch_features_handler(self, ev):
datapath = ev.msg.datapath
ofproto = datapath.ofproto
parser = datapath.ofproto_parser
# install table-miss flow entry
#
# We specify NO BUFFER to max_len of the output action due to
# OVS bug. At this moment, if we specify a lesser number, e.g.,
# 128, OVS will send Packet-In with invalid buffer_id and
# truncated packet data. In that case, we cannot output packets
# correctly.
match = parser.OFPMatch()
actions = [parser.OFPActionOutput(ofproto.OFPP_CONTROLLER,
ofproto.OFPCML_NO_BUFFER)]
self.add_flow(datapath, 1, 0, match, actions)
def add_flow(self, datapath, hard_timeout, priority, match, actions):
ofproto = datapath.ofproto
parser = datapath.ofproto_parser
inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS,
actions)]
mod = parser.OFPFlowMod(datapath=datapath, priority=priority,
hard_timeout=hard_timeout,
match=match, instructions=inst)
#print mod.__dict__
datapath.send_msg(mod)
@set_ev_cls(
ofp_event.EventOFPErrorMsg,
[HANDSHAKE_DISPATCHER, CONFIG_DISPATCHER, MAIN_DISPATCHER])
def error_msg_handler(self, ev):
msg = ev.msg
self.logger.debug(
'OFPErrorMsg received: type=0x%02x code=0x%02x '
'message=%s', msg.type, msg.code, utils.hex_array(msg.data))
@set_ev_cls(ofp_event.EventOFPPacketIn, MAIN_DISPATCHER)
def _packet_in_handler(self, ev):
...
def send_packet_out(self, msg, actions):
datapath = msg.datapath
ofproto = datapath.ofproto
parser = datapath.ofproto_parser
in_port = msg.match['in_port']
data = None
if msg.buffer_id == ofproto.OFP_NO_BUFFER:
data = msg.data
out = parser.OFPPacketOut(datapath=datapath, buffer_id=msg.buffer_id,
in_port=in_port, actions=actions, data=data)
datapath.send_msg(out)
def arp_handler(self, header_list, datapath, in_port, msg_buffer_id)
...
def send_group_mod(self, datapath):
ofp = datapath.ofproto
ofp_parser = datapath.ofproto_parser
port_1 = 3
queue_1 = ofp_parser.OFPActionSetQueue(0)
actions_1 = [queue_1, ofp_parser.OFPActionOutput(port_1)]
port_2 = 2
queue_2 = ofp_parser.OFPActionSetQueue(0)
actions_2 = [queue_2, ofp_parser.OFPActionOutput(port_2)]
weight_1 = 50
weight_2 = 50
watch_port = ofproto_v1_3.OFPP_ANY
watch_group = ofproto_v1_3.OFPQ_ALL
buckets = [
ofp_parser.OFPBucket(weight_1, watch_port, watch_group, actions_1),
ofp_parser.OFPBucket(weight_2, watch_port, watch_group, actions_2)]
group_id = 50
req = ofp_parser.OFPGroupMod(
datapath, ofp.OFPFC_ADD,
ofp.OFPGT_SELECT, group_id, buckets)
datapath.send_msg(req)
注：基于RYU应用开发之负载均衡的代码已经放在github上，感兴趣的可以到github上获取应用。
作者简介：
李呈，2014/09-至今，北京邮电大学网络技术研究院 网络与交换技术国家重点实验室攻读硕士研究生
点击可以阅读原文