I have writen a windows service that overwrite Logon and Logoff methods of ISenesLogon2 to check out when logon and logoff occure and then insert the log information into the sql server on server computer.
But it has problem when i turn on the client computer just after the server.
In this situation my service could not insert in sql server.
I think it's because of that the sql server did not load completely before the winservice tried to access to it.
So i want to find a way to check programmatically if the sql server is ready and then try to work with?
Your service cant start until its dependencies remote or otherwise have also started. Checking SQL Server is easy, try and connect to it and retry until you succeed.
Only problem is services have timeouts on startup, you cant sit and repeat this indefinitely.
Things that cannot be reliably started in a reasonable timeframe should not be services or they should fail as soon as possible. Otherwise you will end up with a lot of support requests for your service timing out.
Services are also usually not interactive to the user, so the failure is worse because you cant directly tell the user that your not up unless you do a tray icon.
Related
We are attempting to deploy a SignalR site on a Citrix NetScaler, as opposed to the current deployment on a single server. There are three servers in the farm. If you navigate to any single server, SignalR comes up fine. If you go to the NetScaler address, you get this:
WebSocket connection to
'wss://mysite.com/myapp/signalr/connect?transport=webSockets&clientProtocol=1.5&connectionToken=(token_displayed_here)'
failed: Error during WebSocket handshake: net::ERR_CONNECTION_RESET
After this error, there is about a 10-15 second delay, then it starts working. If I attempt to disable websockets as I have read that Netscalers still have issues with them, the error goes away but the delay remains. I believe the delay is caused by it trying to connect with ServerSentEvents and failing that as well. It appears that only long polling may be working over the NetScaler.
We have checked the NetScaler websocket settings, made sure the servers have the correct machine keys, had a backplane set up (tried Redis and an Oracle Nuget package as that's our typical DB), checked the OWIN versions and web.config settings, all of the stuff that Google told me to do that I could find but still get this error and delay. One thing that I did find is that Netscalers have issues with wss, but haven't been able to find anything about how to account for this. Most of the information found was for people using other load balancing technology.
Is using SignalR (or more specifically, WebSockets or ServerSentEvents) with a NetScaler even doable, and if so what could be causing this problem?
My goal is to send an email out every 5 min from my application even if there isn't a browser open to the application.
I'm using FluentScheduler to manage the tasks; which works up until the server decides to kill the application from inactivity.
My big constraints are:
I can't touch the server. It is how it is and I have to work around it.
I can't rely on a client refreshing a browser or anything else along the lines of using client side scripts.
I can't use any scheduler that uses a database.
What I have been focusing on is trying to create an artificial postback.
Note: The server is load balanced, so a solution could use that
Is there any way that I can keep my application from getting killed by the server?
You could use a monitoring service like https://www.pingdom.com/ to ping the server at regular intervals. Just make sure it hits an endpoint that invokes .NET code and not a static resource.
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 am developing an application (Delphi 7, windows XP) that uses a connection to a remote SQL Server. Sometimes, that server is down, and I want to do something to start it. I was trying to start SQL Server in a local context, and it was fine, it worked... But the point is that I have to start it up from a remote machine.
I can see SQL Server status from a remote server, but I can't start it up... Maybe it gets problems because of user and password, but where to specify the login to the remote machine?
Do you have any idea to do this???
I am sorry about my English.
Thanks.
1) Use sc.exe from a batch file
2) Use the Service Control Manager API via code. You may need to change the process security context (i.e. calling ImpersonateLoggedOnUser) to be able to perform the desired operation, using the right user credentials.
Use OpenSCManager to obtain a handle to the (remote machine's) Service Control Manager, then use OpenService to get a handle to the SQL Server Service, finally use StartService to Start it.
If you want to do this under another account you can use the WNetAddConnection(2) function to connect with credentials (eg to \\machine\ipc$ or \\machine\admin$).
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?