When you start the loadbalancer.org appliance you will see the following:
Default login:
Username: root
Password: loadbalancer
Access to webclient from an external client is:
http://192.168.1.129:9080
http://192.168.1.129:9443
You can access the web administrator using the IP and ports described onscreen.
For the sri lanka porject we are looking for performance and the network diagram indicates we are happy to have the cluster on the same subnet as the rest of the network.
Direct routing is the fasted performance possible, it has the advantage over NAT that the Loadbalancer does not become a bottleneck for incoming and outgoing packets. With DR the loadbalancer simply examines incoming packets and the servers to route the packets directly back to the requesting user.
The web interfaceis the only way to fully configure the loadbalancer vm. The console tool lbwizard will get it initiallised and any further configurations can then be done via the webinterface.
Using lbwizard for the Sri lanka configuration follow these steps.
On the first Loadbalancer:
//Start
Is this unit part for a HA Pair?
YES
Have you already setup the Slave?
NO
Is this a one-armed configuration?
YES
Enter the IP Address for the interface eth0?
Enter IP address you wish to be assigned to the SLAVE loadbalancer.
Enter the netmask for interface eth0?
Enter netmask for the subnet.
Enter the Floating IP adrress?
Enter the IP address that will be IP assosiacted the the HA-pair of loadbalancers.
//Finish
On the 2nd loadbalancer VM, run the lbwizard.
//Start
Is this unit part of an HA-Pair?
YES
Have you already set up the Slave?
YES
What is the slave units UP address?
Enter the IP which you entered when configuring the other loadbalancer VM.
Is this a one-armed configuration?
YES
Enter the IP Address for the interface eth0?
Enter the IP that will be assigned to the MASTER loadbalancer
Enter the netmask for interface eth0?
Enter the subnet netmask.
Enter the Floating IP address?
Enter the IP address that will be IP assosiacted the the HA-pair of loadbalancers.
Enter the address of the default gateway?
Enter the deafult gateway for the subnet.
Enter the IP of the nameserver?
Enter the dns server.
Enter the port for the first Virtual server?
Enter 22 for ssh
Enter the IP address of the first real server?
Enter the real IP of the first appserver
//Finish
Now this is complete we need to go to the web admin interface to configure the 2nd Real Server. As the lbwizard program will only allow you to configure 1 real server.
Now login to the web admin using the default password:
username: loadbalancer
password: loadbalancer
Note: Connect to the IP you have now set for your master loadbalancer
Goto the edit configuration tab
Now click add a real server:
Enter a label
IP address of the server plus the port of the service i.e. 192.168.1.125:22
Edit Configuration -> Virtual Servers
persistancte -> NO
Scheduler-> LC
LC - Least-Connection: assign more jobs to real servers with
fewer active jobs.
Service to check -> custom1
Check port -> 22
Forwarding Method -> DR
Feedback Method -> Agent
Arp Problem when using DR
Every real server must be configured to respond to the VIP address as well as the RIP
address.
You can use iptables (netfilter) on the real server to re-direct incoming packets destined for the virtual
server IP address.
This is a simple case of adding the following command to your start up script (rc.local):
//replace 10.0.0.21 with the Virtual Server IP
iptables -t nat -A PREROUTING -p tcp -d 10.0.0.21 -j REDIRECT
chkconfig iptables on
In this article Yvonne Milne looks at the use of the Recital Remote Data Connectivity Functions with Recital Database Gateways.
If when your attempt to create device meta-data fails this is drbd preventing you from corrupting a file system present on the target partition.
$ drbdadm create-md drbd0
v08 Magic number not found
md_offset 30005817344
al_offset 30005784576
bm_offset 30004867072
Found ext2 filesystem which uses 190804004 kB
current configuration leaves usable 29301628 kB
Device size would be truncated, which
would corrupt data and result in
'access beyond end of device' errors.
You need to either
* use external meta data (recommended)
* shrink that filesystem first
* zero out the device (destroy the filesystem)
Operation refused.
Command 'drbdmeta /dev/drbd0 v08 /dev/sda4 internal create-md' terminated with exit code 40
drbdadm aborting
Once you have confirmed that the file system present on the target partition is no longer required at the prompt type the following:
Replace /dev/sdaX with the block device you are targeting.
dd if=/dev/zero of=/dev/sdaX bs=1M count=128
Once this has completed the drbdadm create-md drbd0 command will complete with a "success."
$ drbdadm create-md drbd0
v08 Magic number not found
v07 Magic number not found
v07 Magic number not found
v08 Magic number not found
Writing meta data...
initialising activity log
NOT initialized bitmap
New drbd meta data block successfully created.
success
$
It would appear that gigabit LAN is not! In fact it often runs at the same speed as 100Mbps LAN. Let's look at why exactly.
After configuring your network you can use the ifconfig command to see what speeds the LAN is connected. Even though 1000Mbps is reported by the card, the reality is that the overall throughtput may well be ~100Mpbs. You can try copying a large file using scp to demonstrate this.
As it turns out, in order to use a gigabit LAN you need to use CAT6 cables. CAT5 and CAT5E are not good enough. End result, the ethernet cards throttle back the speed to reduce dropped packets and errors.
You can find a good article here titled Squeeze Your Gigabit NIC for Top Performance. After tuning up the TCP parameters i found that it made no dfifference. The principal reasons behind low gigabit ethernet performance can be summed up as follows.
- Need to use CAT6 cables
- Slow Disk speed
- Limitations of the PCI bus which the gigabit ethernet cards use
You can get an idea about the disk speed using the hdparm command:
Display the disk partitions and choose the main linux partition which has the / filesystem.
# fdisk -l
Then get disk cache and disk read statistics:
# hdparm -Tt /dev/sda0
On my desktop system the sata disk perfomance is a limiting factor. These were the results:
/dev/sda1:
Timing cached reads: 9984 MB in 2.00 seconds = 4996.41 MB/sec
Timing buffered disk reads: 84 MB in 3.13 seconds = 58.49 MB/sec
Well, that equates to a raw disk read speed of 58.49 * 8 = 467Mbps which is half the speed of a gigabit LAN.
So.. NAS storage with lots of memory looks to be the way to go... If you use the right cables!
In this article Barry Mavin, CEO and Chief Software Architect for Recital, details how to work with Triggers in the Recital Database Server.
Overview
A trigger is a special kind of stored procedure that runs when you modify data in a specified table using one or more of the data modification operations: UPDATE, INSERT, or DELETE.
Triggers can query other tables and can include complex SQL statements. They are primarily useful for enforcing complex business rules or requirements. For example, you can control whether to allow a new order to be inserted based on a customer's current account status.
Triggers are also useful for enforcing referential and data integrity.
Triggers can be used with any data source that is handled natively by the Recital Database Engine. This includes Recital, FoxPro, FoxBASE, Clipper, dBase, CISAM, and RMS data,
Creating and Editing Triggers
To create a new Trigger, right-click the Procedures node in the Databases tree of the Project Explorer and choose Create. To modify an existing Trigger select the Trigger in the Databases Tree in the Project Explorer by double-clicking on it, or select Modify from the context menu. By convertion we recommend that you name your Stored Procedures beginning with "sp_xxx_", user-defined functions with "f_xxx_", and Triggers with "dt_xxx_", where xxx is the name of the table that they are associated with.
Associating Triggers with a Table
Once you have written your Triggers as detailed above you can associate them with the operations performed on a Table by selecting the Table tab.
The Tables tab allows you to select a Trigger procedure by clicking on the small button at the right of the Text field.
Types of Triggers
As can be seen from the Tables tab detailed below, The Recital Database Server handles 6 distinct types of Triggers.
Open Trigger
The Open Trigger is called after is a table is opened but before any operations are performed on it. You can use this trigger to record a log of table usage or provide a programmable means of checing security. If the Trigger procedure returns .F. (false), then the table is not opened. You can use a TRY...CATCH block around the associated command to inform the user.
Close Trigger
The Close Trigger is called just prior to a table being closed. In this trigger you may find it useful to get transaction counts by using the IOSTATS() built-in 4GL function, and record these values in a transaction log.
Update Trigger
The Update Trigger is called prior to a record update operation being performed. You can use this trigger to perform complex application or data specific validation. If the Trigger procedure returns .F. (false), then the record is not updated. You can use inform the user from within the Trigger procedure the reason that the data cannot be updated.
Delete Trigger
The Delete Trigger is called prior to a record delete operation being performed. You can use this trigger to perform complex application or data specific validation such as cross-table lookups e.g. attempting to delete a customer recortd when there are still open orders for that specific customer. If the Trigger procedure returns .F. (false), then the record is not deleted.
Insert Trigger
The Insert Trigger is called prior to a record insert (append) operation being performed. You can use this trigger to perform such tasks as setting up default values of columns within the record. If the Trigger procedure returns .F. (false), then the record is not inserted.
Rollback Trigger
The RollbackTrigger is called prior to a rollback operation being performed from within a form. If the Trigger procedure returns .F. (false), then the record is not rolled back to its original state.
Testing the Trigger
To test run the Trigger, select the Trigger in the Databases Tree in the Project Explorer by double-clicking on it. Once the Database Administrator is displayed, click the Run button to run the Trigger.
The getUIComponentBitmapData method can create bitmapdata for a given IUIComponent. Pass any UIcomponent to get its respective bitmapdata.
public static function getUIComponentBitmapData(target:IUIComponent):BitmapData {
var resultBitmapData:BitmapData = new BitmapData(target.width, target.height);
var m:Matrix = new Matrix();
resultBitmapData.draw(target, m);
return resultBitmapData;
}
Now convert the bitmapdata to a jpeg bytearray.
private static function encodeToJPEG(data:BitmapData, quality:Number = 75):ByteArray {
var encoder:JPGEncoder = new JPGEncoder(quality);
return encoder.encode(data);
}
Now encode the ByteArray into Base64.
public static function base64Encode(data:ByteArray):String {
var encoder:Base64Encoder = new Base64Encoder();
encoder.encodeBytes(data);
return encoder.flush();
}
Upload the base64 encoded ByteArray to the server.
public static uploadData():void {
var url:String = "saveFile.php";
var urlRequest:URLRequest = new URLRequest(url);
urlRequest.method = URLRequestMethod.POST;
var urlLoader:URLLoader = new URLLoader();
var urlVariables:URLVariables = new URLVariables();
urlVariables.file = jpgEncodedFile; // as returned from base64Encode()
urlLoader.data = urlVariables;
urlLoader.load(urlRequest);
}
The saveFile.php file on the server.
Here is a simple shell script to copy your ssh authorization key to a remote machine so that you can run ssh and scp without having to repeatedly login.
#!/bin/sh
# save in file ssh_copykeyto.sh then chmod +x ssh_copykeyto.sh
KEY="$HOME/.ssh/id_rsa.pub"
if [ ! -f ~/.ssh/id_rsa.pub ];then
echo "private key not found at $KEY"
echo "create it with "ssh-keygen -t rsa" before running this script
exit
fi
if [ -z $1 ];then
echo "Bad args: specify user@host as the first argument to this script"
exit
fi
echo "Copying ssh authorization key to $1... "
KEYCODE=`cat $KEY`
ssh -q $1 "mkdir ~/.ssh 2>/dev/null; chmod 700 ~/.ssh; echo "$KEYCODE" >> ~/.ssh/authorized_keys; \ chmod 644 ~/.ssh/authorized_keys"
echo "done!"
MQCURMSGS()
Syntax
MQCURMSGS( <expN> )Description
The MQCURMSGS() function returns the current number of unread messages in the queue specified by <expN>Example
mqdes=mqopen("/myqueue")
if (mqdes < 0)
messagebox(strerror()+",errno="+alltrim(str(error())))
return
endif
do while (mqcurmsgs(mqdes) > 0)
mstr=mqreceive(mqdes)
if (empty(mstr))
messagebox(strerror()+",errno="+alltrim(str(error())))
return
endif
messagebox(mstr)
end do
mqclose(mqdes)
When installing nomachine on redhat 5.3 64-bit be sure to:
- Make sure you have installed the 64-bit packages as the 32-bit ones will not work.
- add the hostname to /etc/hosts
- Check "Disable encryption of all traffic" (in configuration / advanced tab)
- add the hostname to /etc/hosts
- make sure the host IP is not specified as 127.0.0.1 line
- Uncheck "Disable encryption of all traffic" (in configuration / advanced tab)