httpd的mpm配置

Question

我在EC2中运行了一个带有5个httpd服务器(Centos 7)的网站，输入是m3.2xlarge。服务器配置了负载均衡器。渐渐地，服务器内存在所有实例中都会越来越高。

例如：

重新启动httpd服务后几秒钟内内存的使用情况：

[centos@ip-10-0-1-77 ~]$ while  sleep 1; do free -m; done
              total        used        free      shared  buff/cache   available
Mem:          29741        2700       26732          36         307       26728
Swap:             0           0           0
              total        used        free      shared  buff/cache   available
Mem:          29741        2781       26651          36         307       26647
Swap:             0           0           0
              total        used        free      shared  buff/cache   available
Mem:          29741        2820       26613          36         307       26609
Swap:             0           0           0
[centos@ip-10-0-1-77 ~]$ 
.
.
.

一小时后我看到的是：

[centos@ip-10-0-1-77 ~]$ free -m
              total        used        free      shared  buff/cache   available
Mem:          29741       29092         363          41         284         346
Swap:             0           0           0

和上面一样，它在一小时内消耗了所有内存(30 an )。

为了避免这种情况，我开始使用worker mpm配置。

下面的配置是我在/etc/httpd/httpd.conf底部添加的。

<IfModule mpm_worker_module>
MaxRequestWorkers 2500
MaxSpareThreads 250
MinSpareThreads 75
ServerLimit 100
StartServers 3
ThreadsPerChild 25
</IfModule>

有人能帮助并建议我在所有实例中正确地使用RAM内存的配置吗？

Answer 1

一个标准的Apache进程占用大约12 MB的RAM。如果您为Apache预留了30 GB，那么服务器限制为100 (=100*12MB=1200MB=1,2GB)就永远无法达到。所以我假设Apache没有占用所有的内存。

是否有涉及到的应用程序或DB？它们可以占用更大的内存。

对于您的servertuning.conf (或httpd.conf，因为您把它放在那里)：

<IfModule mpm_worker_module>
    #max amount of requests one worker handles before it's forced to close, 2,5k seems almost a little low
    MaxRequestsperChild 2500

    #maximum number of worker threads which are kept spare
    #250 seems quite high, but really depends on the traffic you are experiencing, we normally don't use more than 50-75
    MaxSpareThreads 250

    #minimum number of worker threads which are kept spare
    #really high, only useful if you often experience higher bursts of traffic
    #otherwise you should be fine with 15-30, maybe 50 if you experience higher fluctuation -> bigger bursts of requests
    MinSpareThreads 75

    #upper limit on the configurable number of threads per child process
    #you have to increase this if you want more than 64 ThreadsPerChild
    ThreadLimit 64

    #maximum number of simultaneous client connections
    #that is really low! --> increase that, definitely! We run on 1000, so about 12GB max
    MaxClients 100

    #initial number of server processes to start
    #3 is really low, if you expected your server to be flodded with requests the second you start it
    #maybe turn it up a little to around 20 or even 50 if you receive lots of traffic right after a restart
    StartServers 3

    #number of worker threads created by each child proces
    #25 threads per worker is not tooo much, but at some point the administration of xx threads gets more expensive than creating new ones
    #would suggest to leave it at 25 or turn it up to around 40
    ThreadsPerChild 25
</IfModule>

请注意，我将ServerLimit更改为MaxClients，将MaxRequestWorkers更改为MaxRequestsPerChild，因为据我所知，这是mpm-worker中使用的术语。

此外，还可以更改以下变量：

#KeepAlive: Whether or not to allow persistent connections (more than
#one request per connection). Set to "Off" to deactivate.
#if it's on, leave it there
KeepAlive On

#MaxKeepAliveRequests: The maximum number of requests to allow
#during a persistent connection. Set to 0 to allow an unlimited amount.
#We recommend you leave this number high, for maximum performance.
#default=100, but you can turn that up if your sites contain a lot of item (img, css, ...)
#we are using about 20*<average object-count per site> = 600
MaxKeepAliveRequests 600

#KeepAliveTimeout: Number of seconds to wait for the next request from the
#same client on the same connection.
#would recommend to decrease that, otherwise you could become a victim of slow-dos attacks
#default is 15, we are running just fine on 5
KeepAliveTimeout 5

为了进一步防止缓慢拒绝服务或打开会话的堆积，可以使用mod_reqtimeout。

<IfModule mod_reqtimeout.c>
  # allow 10s timeout for the headers and allow 1s more until 20s upon receipt of 1000 bytes.
  # almost the same with the body, except that it is tricky to
  # limit the request timeout within the body at all - it may take time to generate the body.
  # below are the default values
  #RequestReadTimeout header=10-20,MinRate=1000 body=20,MinRate=1000
  # and this is how I'd set them with today's internet speed
  # deduct the according numbers from explanation above...
  RequestReadTimeout header=2-5,MinRate=100000 body=5-10,MinRate=1000000
</IfModule>

如果这还不足以帮助解决内存问题(如果这些问题确实是由Apache引起的)，那么就使用服务器操作系统的工具来找出占用所有RAM -> 工具的原因。