用python獲取snmp信息有多個現成的庫可以使用，其中比較常用的是netsnmp和pysnmp兩個庫。網上有較多的關于兩個庫的例子。
本文重點在于如何并發的獲取snmp的數據，即同時獲取多臺機器的snmp信息。
netsnmp
先說netsnmp。python的netsnmp，其實是來自于net-snmp包。
python通過一個c文件調用net-snmp的接口獲取數據。
因此，在并發獲取多臺機器的時候，不能夠使用協程獲取。因為使用協程，在get數據的時候，協程會一直等待net-snmp接口返回數據，而不會像socket使用時那樣在等待數據時把CPU切換給其他協程使用。從這點上來說，使用協程和串行獲取沒有區別。
那么如何解決并發獲取的問題呢？可以使用線程，多線程獲取(當然也可以使用多進程)。多個線程同時調用net-snmp的接口獲取數據，然后cpu在多個線程之間不停切換。當一個線程獲取一個結果后，可以繼續調用接口獲取下一個snmp數據。
這里我寫了一個樣例程序。首先把所有的host和oid做成任務放到隊列里，然后啟動多個線程，去執行獲取任務。程序樣例如下：
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import threadingimport timeimport netsnmpimport Queuestart_time = time.time()hosts = ["192.20.150.109", "192.20.150.110", "192.20.150.111", "192.20.150.112", "192.20.150.113", "192.20.150.114", "192.20.150.115", "192.20.150.116", "192.20.150.117", "192.20.150.118", "192.20.150.119", "192.20.150.120", "192.20.150.121", "192.20.80.148", "192.20.80.149", "192.20.96.59", "192.20.82.14", "192.20.82.15", "192.20.82.17", "192.20.82.19", "192.20.82.12", "192.20.80.139", "192.20.80.137", "192.20.80.136", "192.20.80.134", "192.20.80.133", "192.20.80.131", "192.20.80.130", "192.20.81.141", "192.20.81.140", "192.20.82.26", "192.20.82.28", "192.20.82.23", "192.20.82.21", "192.20.80.128", "192.20.80.127", "192.20.80.122", "192.20.81.159", "192.20.80.121", "192.20.80.124", "192.20.81.151", "192.20.80.118", "192.20.80.119", "192.20.80.113", "192.20.80.112", "192.20.80.116", "192.20.80.115", "192.20.78.62", "192.20.81.124", "192.20.81.125", "192.20.81.122", "192.20.81.121", "192.20.82.33", "192.20.82.31", "192.20.82.32", "192.20.82.30", "192.20.81.128", "192.20.82.39", "192.20.82.37", "192.20.82.35", "192.20.81.130", "192.20.80.200", "192.20.81.136", "192.20.81.137", "192.20.81.131", "192.20.81.133", "192.20.81.134", "192.20.82.43", "192.20.82.45", "192.20.82.41", "192.20.79.152", "192.20.79.155", "192.20.79.154", "192.25.76.235", "192.25.76.234", "192.25.76.233", "192.25.76.232", "192.25.76.231", "192.25.76.228", "192.25.20.96", "192.25.20.95", "192.25.20.94", "192.25.20.93", "192.24.163.14", "192.24.163.21", "192.24.163.29", "192.24.163.6", "192.18.136.22", "192.18.136.23", "192.24.193.2", "192.24.193.19", "192.24.193.18", "192.24.193.11", "192.20.157.132", "192.20.157.133", "192.24.212.232", "192.24.212.231", "192.24.212.230"]oids = [".1.3.6.1.4.1.2021.11.9.0",".1.3.6.1.4.1.2021.11.10.0",".1.3.6.1.4.1.2021.11.11.0",".1.3.6.1.4.1.2021.10.1.3.1", ".1.3.6.1.4.1.2021.10.1.3.2",".1.3.6.1.4.1.2021.10.1.3.3",".1.3.6.1.4.1.2021.4.6.0",".1.3.6.1.4.1.2021.4.14.0", ".1.3.6.1.4.1.2021.4.15.0"]myq = Queue.Queue()rq = Queue.Queue()#把host和oid組成任務for host in hosts: for oid in oids: myq.put((host,oid))def poll_one_host(): while True: try: #死循環從隊列中獲取任務，直到隊列任務為空 host, oid = myq.get(block=False) session = netsnmp.Session(Version=2, DestHost=host, Community="cluster",Timeout=3000000,Retries=0) var_list = netsnmp.VarList() var_list.append(netsnmp.Varbind(oid)) ret = session.get(var_list) rq.put((host, oid, ret, (time.time() - start_time))) except Queue.Empty: breakthread_arr = []#開啟多線程num_thread = 50for i in range(num_thread): t = threading.Thread(target=poll_one_host, kwargs={}) t.setDaemon(True) t.start() thread_arr.append(t)#等待任務執行完畢for i in range(num_thread): thread_arr[i].join()while True: try: info = rq.get(block=False) print info except Queue.Empty: print time.time() - start_time break |
netsnmp除了支持get操作之外，還支持walk操作，即遍歷某個oid。
但是walk使用的時候需要謹慎，以免導致高延時等問題，具體可以參見之前的一篇snmpwalk高延時問題分析的博客。
pysnmp
pysnmp是用python實現的一套snmp協議的庫。其自身提供了對于異步的支持。
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import timeimport Queuefrom pysnmp.hlapi.asyncore import *t = time.time()myq = Queue.Queue()#回調函數。在有數據返回時觸發def cbFun(snmpEngine, sendRequestHandle, errorIndication, errorStatus, errorIndex, varBinds, cbCtx): myq.put((time.time()-t, varBinds))hosts = ["192.20.150.109", "192.20.150.110", "192.20.150.111", "192.20.150.112", "192.20.150.113", "192.20.150.114", "192.20.150.115", "192.20.150.116", "192.20.150.117", "192.20.150.118", "192.20.150.119", "192.20.150.120", "192.20.150.121", "192.20.80.148", "192.20.80.149", "192.20.96.59", "192.20.82.14", "192.20.82.15", "192.20.82.17", "192.20.82.19", "192.20.82.12", "192.20.80.139", "192.20.80.137", "192.20.80.136", "192.20.80.134", "192.20.80.133", "192.20.80.131", "192.20.80.130", "192.20.81.141", "192.20.81.140", "192.20.82.26", "192.20.82.28", "192.20.82.23", "192.20.82.21", "192.20.80.128", "192.20.80.127", "192.20.80.122", "192.20.81.159", "192.20.80.121", "192.20.80.124", "192.20.81.151", "192.20.80.118", "192.20.80.119", "192.20.80.113", "192.20.80.112", "192.20.80.116", "192.20.80.115", "192.20.78.62", "192.20.81.124", "192.20.81.125", "192.20.81.122", "192.20.81.121", "192.20.82.33", "192.20.82.31", "192.20.82.32", "192.20.82.30", "192.20.81.128", "192.20.82.39", "192.20.82.37", "192.20.82.35", "192.20.81.130", "192.20.80.200", "192.20.81.136", "192.20.81.137", "192.20.81.131", "192.20.81.133", "192.20.81.134", "192.20.82.43", "192.20.82.45", "192.20.82.41", "192.20.79.152", "192.20.79.155", "192.20.79.154", "192.25.76.235", "192.25.76.234", "192.25.76.233", "192.25.76.232", "192.25.76.231", "192.25.76.228", "192.25.20.96", "192.25.20.95", "192.25.20.94", "192.25.20.93", "192.24.163.14", "192.24.163.21", "192.24.163.29", "192.24.163.6", "192.18.136.22", "192.18.136.23", "192.24.193.2", "192.24.193.19", "192.24.193.18", "192.24.193.11", "192.20.157.132", "192.20.157.133", "192.24.212.232", "192.24.212.231", "192.24.212.230"]oids = [".1.3.6.1.4.1.2021.11.9.0",".1.3.6.1.4.1.2021.11.10.0",".1.3.6.1.4.1.2021.11.11.0",".1.3.6.1.4.1.2021.10.1.3.1", ".1.3.6.1.4.1.2021.10.1.3.2",".1.3.6.1.4.1.2021.10.1.3.3",".1.3.6.1.4.1.2021.4.6.0",".1.3.6.1.4.1.2021.4.14.0", ".1.3.6.1.4.1.2021.4.15.0"] snmpEngine = SnmpEngine()#添加任務for oid in oids: for h in hosts: getCmd(snmpEngine, CommunityData('cluster'), UdpTransportTarget((h, 161), timeout=3, retries=0,), ContextData(), ObjectType(ObjectIdentity(oid)), cbFun=cbFun)time1 = time.time() - t#執行異步獲取snmpsnmpEngine.transportDispatcher.runDispatcher()#打印結果while True: try: info = myq.get(block=False) print info except Queue.Empty: print time1 print time.time() - t break |
pysnmp本身只支持最基礎的get和getnext命令，因此如果想使用walk，需要自己進行實現。
在同一個環境下，對兩者進行了性能測試。兩者對198個host，10個oid進行采集。
| 測試組 | 耗時(sec) |
|---|---|
| netsnmp(20線程) | 6.252 |
| netsnmp(50線程) | 3.269 |
| netsnmp(200線程) | 3.265 |
| pysnmp | 4.812 |
可以看到netsnmp的采集速度跟線程數有關。當線程數增大到一定程度，采集時間不再縮短。因為開辟線程同樣會消耗時間。而已有的線程已經足夠處理。
pysnmp性能較之略差一下。詳細分析pysnmp在添加任務(執行getCmd時)消耗了約1.2s，之后的采集約消耗3.3秒。
在增加了oid數，在進行實驗。host仍然是198個，oid是42個。
| 測試組 | 耗時(sec) |
|---|---|
| netsnmp(20線程) | 30.935 |
| netsnmp(50線程) | 12.914 |
| netsnmp(200線程) | 4.044 |
| pysnmp | 11.043 |
可以看到差距被進一步拉大。在線程足夠多的情況下，netsnmp的效率要明顯強于pysnmp。
因為二者都支持可以并行采集多個host，從易用性來說，netsnmp更為簡單一些，且netsnmp支持walk功能。本文更加推薦netsnmp。
安裝netsnmp需要安裝net-snmp。如果centos，則使用yum會較為方便。
以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持服務器之家。
原文鏈接：http://www.cnblogs.com/xuxinkun/p/5647715.html
