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advice about a network app

 
 
cartercc@gmail.com
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      03-21-2007
Sorry, but Java isn't my language, so I'm showing my ignorance.

My assignment is to create a number (35-40) client apps on a network
segment that will communicate with a server that also resides on the
segment. The clients accept queries from the server and reply to the
server. Queries are like, 'How many cases have you processed this
hour?, and replies can be an integer from 0 on up. The language in the
spec is Java.

The part that stumps me is building an application that will actually
place a client on a node and start it. I'm thinking about something
like this:

public static void main(String[] args) {
read configuration file that has the node name, IP addresse
and port of the network nodes
// each line looks like this: node1:192.168.100.1:9876
String line = readline();
ServerNode sn = new ServerNode(line);
start(sn);
line = readline();
while (line =! null) {
ClientNode cn = new ClientNode(line);
deploy cn to appropriate machine depending on IP
address;
start(cn);
line = readline();
}
}

Unfortunately, I'm having trouble getting started. Any suggestions as
to here to look? I don't have physical access to each machine to
deploy each client. Each node is gauranteed to have a JVM.

Thanks, CC.
}

 
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Oliver Wong
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      03-21-2007
<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ups.com...
> Sorry, but Java isn't my language, so I'm showing my ignorance.
>
> My assignment is to create a number (35-40) client apps on a network
> segment that will communicate with a server that also resides on the
> segment. The clients accept queries from the server and reply to the
> server. Queries are like, 'How many cases have you processed this
> hour?, and replies can be an integer from 0 on up. The language in the
> spec is Java.


In order to best tailor the answer for your situation, can you give
some background information: This sounds like a fairly complicated
project, so why would you try to implement it in a language you're not
familiar with? Is the goal to "practice" or "learn" Java, or is your
boss/client/teacher forcing you to use Java despite your where your skills
lie? Where *do* your skills lie? Have you ever written a distributed
application before? What programming languages are you familiar with? How
familiar are you with the TCP/IP protocol? etc.

>
> The part that stumps me is building an application that will actually
> place a client on a node and start it. I'm thinking about something
> like this:
>
> public static void main(String[] args) {
> read configuration file that has the node name, IP addresse
> and port of the network nodes
> // each line looks like this: node1:192.168.100.1:9876
> String line = readline();
> ServerNode sn = new ServerNode(line);
> start(sn);
> line = readline();
> while (line =! null) {
> ClientNode cn = new ClientNode(line);
> deploy cn to appropriate machine depending on IP
> address;
> start(cn);
> line = readline();
> }
> }
>
> Unfortunately, I'm having trouble getting started. Any suggestions as
> to here to look? I don't have physical access to each machine to
> deploy each client. Each node is gauranteed to have a JVM.


If you're familiar with the TCP/IP protocol, you would probably be
aware that in order to connect to a specific computer and exchange data
with it, that computer needs to be listening on some port, and your
connecting computer would need to specify the port when connecting.

You would also probably be aware that there must be some software on
these listening computers which will do something with the data they
receive from listening to those ports.

What that software is and what is does is critical to being able make
any progress.

- Oliver


 
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cartercc@gmail.com
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      03-21-2007
On Mar 21, 4:42 pm, "Oliver Wong" <(E-Mail Removed)> wrote:
> In order to best tailor the answer for your situation, can you give
> some background information: This sounds like a fairly complicated
> project, so why would you try to implement it in a language you're not
> familiar with? Is the goal to "practice" or "learn" Java, or is your
> boss/client/teacher forcing you to use Java despite your where your skills
> lie? Where *do* your skills lie? Have you ever written a distributed
> application before? What programming languages are you familiar with? How
> familiar are you with the TCP/IP protocol? etc.


I work in an IT department of a large state university. I am a
database guy, and my strength is Perl. I write a lot of file
manipulation scripts, where I input one data file, process it, and
output it in another form. It's all data related, and over the years
we've amassed quite a bit of scripts, undocumented and frankly
unmaintainable. I've written one largish Java app, participated in
about six more, and am probably an advanced beginner/low intermediate
in Java. I don't do network programming, at least not until now.

The order of the day is, move to Java, stop using Perl, convert
everything over. Obviously, we'll continue to do the one-off things in
Perl, but we have several big apps that really do need to be in Java
simply for the sake of maintaining them.


> If you're familiar with the TCP/IP protocol, you would probably be
> aware that in order to connect to a specific computer and exchange data
> with it, that computer needs to be listening on some port, and your
> connecting computer would need to specify the port when connecting.
>


Yeah. My background is as a web developer and server administrator, so
I understand HTTP, TCP/IP, Apache, FTP, CGI, etc. This is where I
learned Perl.

> You would also probably be aware that there must be some software on
> these listening computers which will do something with the data they
> receive from listening to those ports.
>
> What that software is and what is does is critical to being able make
> any progress.


This may sound funny, but it's really a prototype to test the
feasibility of a proposed system. I might not be the guy who should be
doing this, but I'm the guy with the project, and I'm really 'the'
programmer in my department. I don't know the eventual use, but I've
got a real set of requirements -- build an application that will
deploy an (arbitrary) number of clients that will self execute,
listen, and reply to requests. Writing the server was easy, and using
the UDP socket interface wasn't difficult. I'm just stuck on getting
the clients going. I can install and start the client programs on
several machines manually, but that doesn't meet the requirements.

CC

 
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RedGrittyBrick
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Posts: n/a
 
      03-21-2007
http://www.velocityreviews.com/forums/(E-Mail Removed) wrote:
> On Mar 21, 4:42 pm, "Oliver Wong" <(E-Mail Removed)> wrote:
>> In order to best tailor the answer for your situation, can you give
>> some background information: This sounds like a fairly complicated
>> project, so why would you try to implement it in a language you're not
>> familiar with? Is the goal to "practice" or "learn" Java, or is your
>> boss/client/teacher forcing you to use Java despite your where your skills
>> lie? Where *do* your skills lie? Have you ever written a distributed
>> application before? What programming languages are you familiar with? How
>> familiar are you with the TCP/IP protocol? etc.

>
> I work in an IT department of a large state university. I am a
> database guy, and my strength is Perl. I write a lot of file
> manipulation scripts, where I input one data file, process it, and
> output it in another form. It's all data related, and over the years
> we've amassed quite a bit of scripts, undocumented and frankly
> unmaintainable. I've written one largish Java app, participated in
> about six more, and am probably an advanced beginner/low intermediate
> in Java. I don't do network programming, at least not until now.
>
> The order of the day is, move to Java, stop using Perl, convert
> everything over. Obviously, we'll continue to do the one-off things in
> Perl, but we have several big apps that really do need to be in Java
> simply for the sake of maintaining them.
>
>
>> If you're familiar with the TCP/IP protocol, you would probably be
>> aware that in order to connect to a specific computer and exchange data
>> with it, that computer needs to be listening on some port, and your
>> connecting computer would need to specify the port when connecting.
>>

>
> Yeah. My background is as a web developer and server administrator, so
> I understand HTTP, TCP/IP, Apache, FTP, CGI, etc. This is where I
> learned Perl.
>
>> You would also probably be aware that there must be some software on
>> these listening computers which will do something with the data they
>> receive from listening to those ports.
>>
>> What that software is and what is does is critical to being able make
>> any progress.

>
> This may sound funny, but it's really a prototype to test the
> feasibility of a proposed system. I might not be the guy who should be
> doing this, but I'm the guy with the project, and I'm really 'the'
> programmer in my department. I don't know the eventual use, but I've
> got a real set of requirements -- build an application that will
> deploy an (arbitrary) number of clients that will self execute,
> listen, and reply to requests. Writing the server was easy, and using
> the UDP socket interface wasn't difficult. I'm just stuck on getting
> the clients going. I can install and start the client programs on
> several machines manually, but that doesn't meet the requirements.
>


What services are available on the client nodes? ftp? sftp? telnet? sshd?
 
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Lew
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      03-21-2007
Are you able to start apps on the client nodes via an administrative process
or shell script, that is, not using Java? That would simplify things.

Have all new client processes send to the central server and request
instructions, then block until the server replies. The server would maintain a
pool of clients who have "checked in", and send replies (only) to those to
whom it must issue instructions. Then it does nothing with that client until
it next sends its "I'm ready" message.

That way the server never needs to know how many clients are out there until
they are ready. It never needs to know where they are, or what ports are open.
There is one server host (or cluster) with a well-known single open port. This
is much simpler than managing a geometrically increasing web of clients.

Keep the server "always" running (as a server should be). The clients report
in whenever they are available. Multiple client instances can run on a single
machine, which helps in testing.

-- Lew

 
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