MaxTotalConnections and MaxConnectionPerRoute in case of httpclient instance per target host

[Brijesh Deo <bd...@SonicWALL.com>]

Hi,

 

I am implementing an http reverse proxy, somewhat on the lines of the
sample implementation - ElementalReverseProxy with some modifications. I
am using HttpCore classes to implement the http server (using
org.apache.http.protocol.HttpService) and the HttpClient api (instead of
the HttpRequestExecutor) to implement the client side for sending the
Http requests to the target servers and receiving Http Responses from
them. I am using the latest HttpClient 4.0 binaries bundle (with
dependencies).

 

I need to provide access to several backend http web-servers through my
reverse proxy. For that, I am creating one HttpClient instance per
backend host and all requests targeted to a particular target host are
executed using the corresponding httpClient instance. Every httpClient
instance uses separate instances of ThreadSafeClientConnManager. Every
HttpClient-ThreadSafeClientConnManager pair has MaxTotalConnections = 20
and MaxConnectionsPerRoute = 10.

 

With respect to this I have the following questions:

 

1) Since I have one HttpClient-ThreadSafeClientConnManager instances
pair for one target host, can there be multiple routes (HttpRoute) to
the same target server while executing requests from the HttpClient? Or
would there be only one route to a given target host in this case?

 

2) I have noticed that when multiple threads are executing requests to a
given target server using the corresponding HttpClient instance, I get
ConnectionPoolTimeoutException at times when the no of connections
touches MaxConnectionsPerRoute (10) even though the MaxTotalConnections
is 20. So, do all the connections use the same route in such scenarios?
Then, in cases like these MaxConnectionsPerRoute becomes the limiting
value for the number of allowed connections rather than the
MaxTotalConnections. Is this observation correct? 

 

3) In cases like this, do the two parameters MaxTotalConnections and
MaxConnectionPerRoute need to have the same value?

 

Please help in understanding/ validating this assumption.

 

Thanks,

Brijesh

Re: MaxTotalConnections and MaxConnectionPerRoute in case of httpclient instance per target host

[Oleg Kalnichevski <ol...@apache.org>]

On Mon, Aug 17, 2009 at 12:37:37AM +0530, Brijesh Deo wrote:
> Hi,
> 
>  
> 
> I am implementing an http reverse proxy, somewhat on the lines of the
> sample implementation - ElementalReverseProxy with some modifications. I
> am using HttpCore classes to implement the http server (using
> org.apache.http.protocol.HttpService) and the HttpClient api (instead of
> the HttpRequestExecutor) to implement the client side for sending the
> Http requests to the target servers and receiving Http Responses from
> them. I am using the latest HttpClient 4.0 binaries bundle (with
> dependencies).
> 
>  
> 
> I need to provide access to several backend http web-servers through my
> reverse proxy. For that, I am creating one HttpClient instance per
> backend host and all requests targeted to a particular target host are
> executed using the corresponding httpClient instance. Every httpClient
> instance uses separate instances of ThreadSafeClientConnManager. Every
> HttpClient-ThreadSafeClientConnManager pair has MaxTotalConnections = 20
> and MaxConnectionsPerRoute = 10.
> 
> 

I personally see no benefit of having multiple HttpClient / ConnectionManager,
(a pair per target host). A single HttpClient instance with
ThreadSafeClientConnManager would do the job just as well.

 
> 
> With respect to this I have the following questions:
> 
>  
> 
> 1) Since I have one HttpClient-ThreadSafeClientConnManager instances
> pair for one target host, can there be multiple routes (HttpRoute) to
> the same target server while executing requests from the HttpClient? Or
> would there be only one route to a given target host in this case?
> 
> 

Only one route, provide you do not use different proxies to access the same
target host.

 
> 
> 2) I have noticed that when multiple threads are executing requests to a
> given target server using the corresponding HttpClient instance, I get
> ConnectionPoolTimeoutException at times when the no of connections
> touches MaxConnectionsPerRoute (10) even though the MaxTotalConnections
> is 20. So, do all the connections use the same route in such scenarios?

Apparently, they do

> Then, in cases like these MaxConnectionsPerRoute becomes the limiting
> value for the number of allowed connections rather than the
> MaxTotalConnections. Is this observation correct? 
> 
>  

Yes, it is


> 
> 3) In cases like this, do the two parameters MaxTotalConnections and
> MaxConnectionPerRoute need to have the same value?
> 
>  

No, they do not, but the exact setup depends on particular needs of your
applications.

For instance one many want to ensure that there is no more than 10 connections
to Host A and no more than 10 connections to Host B, but simultameously there
is no more than 15 connections in total at the same time.

Oleg

> 
> Please help in understanding/ validating this assumption.
> 
>  
> 
> Thanks,
> 
> Brijesh
> 

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