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Delphi Client-Server Application using Firebird 2.5 embedded connection error
I have got a lengthy question to ask. First of all Im still very new when it comes to Delphi programming and my experience has beem mostly developing small single user database applications using ADO and an Access database.
I need to take the transition now to a client server application and this is where the problem starts. I decided to use Firebird 2.5 embeded as my database, as it is open source, and it is can be used with the interbase components in Delphi and that multiple clients can access the database simultanously. So I followed the interbase tutorial in Delphi. I managed to connect the client to the server and see the data in the example (While both are running on my pc), but when i tried to move the client to another pc, keeping the server on mine and running it to see if I can connect to the server it gave me the following error.
Exception EIdSocketError in module clientDemo.exe at 0029DCAC. Socket Error # 10061 Connection refused.
I understand that this might be because the host is defined as localhost in the client. But here is my first question. In the TSQLConncetion you can set die hostname under Driver->Hostname. The thing I want to know is how do you do this at run time, as I cannot get the property when I try and make an edit box to allow the user to enter the value and then set it via code like for example:
SQLConncetion1.Driver.Hostname := edtHost.text;
The thing is there is not such property to set, so how do you set the hostname at run time?
Im using Delphi XE2
There is still a lot of questions to come especially when it comes to deployment, but I will take this piece by piece and I appreciate the advice.
That means that the server: port your program is trying to connect to
is refusing your connection. Could be a firewall related issue on
either your server or your own machine.
Try using telent to connect to the server. If that succeeds you know it a problem with your machine's configuration.
Check these links for more information :
How TO Fix Socket Error 10061 Connection Refused Easily
Problem Loading (python blocked by firewall)
Related
I am working with intuit SDK tech support on this without much luck. I was hoping someone here might know what object this error might be referring to.
I am basically sending a request from one computer to QuickBooks on another machine via PowerShell and Remote Data Sharing (RDS) Client/Server provided in the QuickBooks SDK. The relative portion of the Powershell script looks something like this..
$myQBXMLRP = New-Object -com QBXMLRP2.RequestProcessor
$myQBXMLRP.OpenConnection2("qb4D","CCFolioPro",2)
The first line instantiates the COM object QBXMLRP2.RequestProcessor. The second line opens a connection with QuickBooks. RDS Client on the local machine receives the OpenConnection request and passes it on to the RDS Server on the machine where QB resides which in turn opens the connection with QB. The second line is throwing the following error...
Exception calling "OpenConnection2" with "3" argument(s): "Public key exchange error: Object already exists
Reading here in stackoverflow and elsewhere via google I see that this error occurs to other programmers not dealing in any way with QuickBooks, so I am hoping somone here might be able to help me figure out how to fix the problem.
I have QB/RDS working fine prior to this installation. So I know it should work as is. Something is hung up on this computer, the server computer, or ????
Thanks,
John
Your mileage may vary. I cleared the following file, reboot and reinstall RDS then things are back to normal. It was on a Windows Server 2012 but you get the idea. You need to change your view options so these folders are not hidden. Worths a shot, and I hope this helps.
Clear one of the key files created by RDS by prior runs or installations
I'm using code from a demo program using Devart's MyDac component using Delphi 2009 to connect to a remote database using SSL.
I have made and verified the certificates and keys and set the connection parameters in MyDAC to use them eg
MyConnection.protocol := 'mpSSL';
MyConnection.SSLOptions.CACert := 'C:\ca-cert.pem';
MyConnection.SSLOptions.Cert := 'C:\client-cert.pem';
MyConnection.SSLOptions.Key := 'C:\client-key.pem';
MyConnection.SSLOptions.Chipherlist := 'All';
When I tell MyConnection to connect (after setting the user name / password etc) it connects to the database with no problems.
However as a test I deliberately put in an invalid key name of 'C:\XXXclient-key.pem and it still connected OK so maybe it wasn't using SSL at all.
So my question is:
How can I use Delphi to detect if a connection is really using SSL or not?
I think I'll close this question myself as it seem far more complex than I thought it was and I need much more information before this question makes sense. It appears that the sql statement;
SHOW STATUS LIKE 'Ssl_cipher'
can help as its value will be empty if its not using ssl or will contain an value if it is.
The touble was the Mysql server I was using (ISP Nativespace) did not even have a variable name called Ssl_cipher so it looks like it doesn't support ssl anyway. Trying the same thing using another ISP I did see the variable name but it had no value, showing that was also not using ssl even I though it could do it.
It now appears that there is much more that needs doing before a ssl connection can be set up. Creating a new user on the db that only ever uses ssl, setting up permissions for them, running code on the server etc.
Not at all as simple as Devart's web page on securebridge leads one to believe!
"It is enough to place several components on the form and specify the
server address and the user login information to establish a secure
connection."
Err... not quite!
We've got a mirrored SQL server 2012 database setup on Azure VM's - two servers plus a witness, all using client certificates, with SQL logins with the same SID set.
When testing our app from a different VM, everything works as expected when we manually failover the database, there's a one second wait and then it continues to operate quite happily.
If we then do another manual failover, ie moving the principal back to the original server, the app errors and throws a 'no such host in known' error. Recycling the app pool fixes the issue, but this clearly isn't workable in production when one of the servers is updated followed by the other at some later point (both are in an availability set).
The host not known error is somewhat baffling as it was communicating with it happily before the initial failover, and will again after the app pool recycle.
Here's the connection string as it is right now, after a lot of faffing around:
"Data Source=server1,1433;Failover Partner=server2,1433;Initial
Catalog=;MultipleActiveResultSets=True;User Id=user;
Password=password; Network=dbmssocn;Connect Timeout=60; async = true;"
providerName="System.Data.SqlClient"
The app is running on .net 4.5.2, so should be up to date with hotfixes, and we're out of ideas after much Googling with Bing.
I've just solved a problem that I had that looks very similar to your problem. I'd get the host not known error whenever the database switched from the first one listed in the web.config file to the failover one. It was fine switching from the failover to the primary.
The problem that I had was that I set up the database mirroring using server names but my web server did not know the database servers by name. Once I fixed this, I was able to get the failover working smoothly both ways.
This is what I think was happening:
I set up the mirroring using the names SQL1 and SQL2 as the principal and mirror servers
I have their ip addresses in my connection string: 10.1.1.5 and 10.1.1.6
The application tries to get to the first server 10.1.1.5 and succeeds and is then told that the mirror server is SQL2
SQL1 goes down and the database is successfully switched to the mirror server.
The web application attempts to connect, fails and determines that it should try the second server.
It tries to connect to SQL2, which it doesn't know, and fails with the message that the host is unknown.
This answer would only apply to your situation if you actually put ip addresses in your web.config and that server1,1433 and server2,1433 were actually masking place-holders for the ip addresses that you actually used.
I haven't really solved the naming issue though. I just added the two database server names to the HOSTS file which isn't an acceptable situation but does prove my theory on what my problem was.
I am researching a setup just like you have and upon reading this and the response by Steve Kaye, I'm wondering if you have SQL browser running. Take a look at this article for how SQL browser comes into play:
http://blogs.msdn.com/b/spike/archive/2010/12/15/running-a-database-mirror-setup-with-the-sqlbrowser-service-off-may-produce-unexpected-results.aspx
I have got a lengthy question to ask. First of all Im still very new when it comes to Delphi programming and my experience has beem mostly developing small single user database applications using ADO and an Access database.
I need to take the transition now to a client server application and this is where the problem starts. I decided to use Firebird 2.5 embeded as my database, as it is open source, and it is can be used with the interbase components in Delphi and that multiple clients can access the database simultanously. So I followed the interbase tutorial in Delphi. I managed to connect the client to the server and see the data in the example (While both are running on my pc), but when i tried to move the client to another pc, keeping the server on mine and running it to see if I can connect to the server it gave me the following error.
Exception EIdSocketError in module clientDemo.exe at 0029DCAC. Socket Error # 10061 Connection refused.
I understand that this might be because the host is defined as localhost in the client. But here is my first question. In the TSQLConncetion you can set die hostname under Driver->Hostname. The thing I want to know is how do you do this at run time, as I cannot get the property when I try and make an edit box to allow the user to enter the value and then set it via code like for example:
SQLConncetion1.Driver.Hostname := edtHost.text;
This cannot be done this way and the only way I see you can set the hostname is with the object inspector, but that is not available at runtime and I need to set the hostname on the client when the program is running the first time, so how do you set the hostname/IP address at runtime?
Im using Delphi XE2
There is still a lot of questions to come especially when it comes to deployment, but I will take this piece by piece and I appreciate the advice.
Embedded can't be used by multiple users at the same time (even if it's two applications on the same machine). See here for information on the differences between the three versions. There's also information in another SO question that might help.
As far as specifying a server at runtime, this may help:
procedure TForm1.Button1Click(Sender: TObject);
var
Conn: TSQLConnection;
begin
Conn := TSQLConnection.Create(Self);
try
Conn.DriverName := 'FirebirdConnection';
Conn.Params.Add('User_Name=SYSDBA');
Conn.Params.Add('Password=masterkey');
// Replace the dbname in the next line with the
// value obtained at runtime, as in
// Conn.Params.Add('Database=' + YourNewPathAndDBName);
Conn.Params.Add('Database=C:\FireBirdData\YourDB.fdb');
Conn.Open;
if Conn.Connected then
ShowMessage('Connection successfully made to DB');
finally
Conn.Free;
end;
end;
We use stateful DataSnap servers for some business logic tasks and also to provide clientdataset data.
If we have to update the server to modify a business rule, we copy the new version into a new empty folder and register it (depending on the Delphi version, just by launching or by running the TRegSvr utility).
We can do this even while the old server instance is running. However, after registering the new version, all new client connections will still use the currently running (old) server instance. All clients have to disconnect first, then the new server will be used for the next clients.
Is there a way to direct all new client connections to the new server, immediately after registering?
(I know that new or changed method signatures will also require a change and restart of the clients but this question is about internal modifications which do not affect the interface)
We are using Socket connections, and all clients share the same server application (only one application window is open). In the early days we have used a different configuration of the remote datamodule which resulted in one app window per client. Maybe this could be a solution? (because every new client will launch the currently registered executable)
Update: does Delphi XE offer some support for 'hot deployment' (of updated servers)? We use Delphi 2009 at the moment but would upgrade to XE if it offers easier implementation of 'hot deployment'.
you could separate your appserver into 2 new servers, one being a simple proxy object redirecting all methods (and optionally containing state info if any) to the second one actually implementing your business logic. you also need to implement "silent reconnect" feature within your proxy server in order not to disturb connected clients if you decide to replace business appserver any time you want. never did such design myself before but hope the idea is clear
Have you tried renaming the current server and placing the new in the same location with the correct name (versus changing the registry location). I have done this for COM libraries before with success. I am not sure if it would apply to remote launch rules through as it may look for an existing instance to attach to instead of a completely fresh server.
It may be a bit hackish but you would have the client call a method on the server indicating that a newer version is available. This would allow it to perform any necessary cleanup so it doesn't end up talking to both the existing server instance and new server instance at the same time.
There is probably not a simple answer to this question, and I suspect that you will have to modify the client. The simplest solution I can think of is to have a flag (a property or an out parameter on some commonly called method) on the server that the client checks periodically that tells the client to disconnect and reconnect (called something like ImBeingRetired).
It's also possible to write callbacks under certain circumstances for datasnap (although I've never done this). This would allow the server to inform the client that it should restart or reconnect.
The last option I can think of (that hasn't already been mentioned) would be to make the client/server stateless, so that every time the client wants something it connects, gets what it wants then disconnects.
Unfortunately none of these options are the answer you want to your question, but might give you some ideas.
(optional) set up vmware vSphere, ESX, or find a hosting service that already has one.
Store the session variables in db.
Prepare 2 web boxes with 2 distinct IP address and deploy your stuff.
Set up DNS, firewall, load balancer, or BSD vm so name "example.com" resolves to web box 1.
Deploy new version to web box 2.
Switch over to web box 2 using whatever routing method you chose.
Deploy new version to web box 1 if things look ok.
Using DNS is probably easiest, but it takes time for the mapping to propagate to the client (if the client is outside your LAN) and also two clients may see different results. Some firewalls have IP address mapping feature that you can map public IP address and internal IP address. The ideal way is to use load balancer and configure it to 50:50 and change it to 100:0 when you want to do upgrade, but it costs money. A cheaper alternative is to run software load balancer on BSD vm, but it probably requires some work.
Edit: What I meant to say is session variables, not session. You said the server is stateful. If it contains some business logic that uses session variable, it needs to get stored externally to be preserved across reconnection during switch over. Actual DataSnap session will be lost, so when you shutdown web box 1 during upgrade, the client will get "Session {some-uuid} is not found" error by web box 1, and it will reconnect to web box 2.
Also you could use 3 IP addresses (1 public and 2 private) so the client always sees 1 address , which is better method.
I have done something similar by having a specific table which held my "data version". Each time I would update the server or change a system wide global setting, I would increment this field. When a client starts it always checks this value, and will check again before any transactions/queries. If the value was ever different from when I first started, then I needed to go through my re-initialization logic, which could easily include a re-login to an updated server.
I was using IIS to publish my app servers, so the data that would change would be the path to the app server. I kept the old ones available, to respond to any existing transactions that were in play. Eventually these would be removed once I knew there were no more client connections to that version.
You could easily handle knowing what versions to keep around if you log what server the client last connected too (and therefore would know about).
For newer versions (Delphi 2010 and up), there is an interesting solution
for systems using the HTTP transport:
Implementing Failover and Load Balancing in DataSnap 2010 by Andreano Lanusse
and a related question for the TCP/IP transport:
How to direct DataSnap client connections to various DS Servers?