On exit of an .rsp page.
SAVE DATASESSION TO m_state
_SESSION["state"] = m_state
On entry to an .rsp page.
IF type( _session["state"] ) != "U"
m_state = _session["state"]
RESTORE DATASESSION FROM m_state
ENDIF
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
Opening SSH to the outside world is a security risk. Here is how to restrict SSH access to certain IP addresses on a machine.
- Edit the /etc/hosts.allow file to include these lines, assuming your machine is on the 192.168.2.x nonrouting IP block, and you want to enable an external address of 217.40.111.121 IP block: Remember to add the period on the end of each incomplete IP number. If you have another complete IP address or range, add a space and that range on the end.
sshd,sshdfwd-X11: 192.168.2. 217.40.111.121
- Edit your /etc/hosts.deny file to include this line:
sshd,sshdfwd-X11:ALL
- These lines refuse SSH connections from anyone not in the IP address blocks listed.
Additionally you can restrict SSH access by username.
- Edit the /etc/ssh/sshd_config file and add the following lines
PermitRootLogin no
AllowUsers user1 user2 user3 etc
PasswordAuthentication yes
Now restart the ssh daemon for these changes to take effect
service sshd restart
DRBD:
DRBD (Distributed Replicated Block Device) forms the storage redundancy portition of a HA cluster setup. Explained in basic terms DRBD provides a means of achieving RAID 1 behavoir over a network, where whole block devices are mirrored accross the network.
To start off you will need 2 indentically sized raw drives or partitions. Many how-to's on the internet assume the use of whole drives, of course this will be better performance, but if you are simply getting familar with the technology you can repartition existing drives to allow for two eqaully sized raw partitions, one on each of the systems you will be using.
There are 3 DRBD replication modes:
• Protocol A: Write I/O is reported as completed as soon as it reached local disk and local TCP send buffer
• Protocol B: Write I/O is reported as completed as soon as it reached local disk and remote TCP buffer cache
• Protocol C: Write I/O is reported as completed as soon as it reached both local and remote disks.
If we were installing the HA cluster on a slow LAN or if the geogrphical seperation of the systems involved was great, then I recommend you opt for asyncronous mirroring (Protocol A) where the notifcation of a completed write operation occurs as soon as the local disk write is performed. This will greatly improve performance.
As we are setting up our HA cluster connected via a fast LAN, we will be using DRBD in fully syncronous mode, protocol C.
Protocol C involves the file system on the active node only being notified that the write operation was finished when the block is written to both disks of the cluster. Protocol C is the most commonly used mode of DRBD.
/etc/drbd.conf
global { usage-count yes; }
common { syncer { rate 10M; } }
resource r0 {
protocol C;
net {
max-buffers 2048;
ko-count 4;
}
on bailey {
device /dev/drbd0;
disk /dev/sda4;
address 192.168.1.125:7789;
meta-disk internal;
}
on giskard {
device /dev/drbd0;
disk /dev/sda3;
address 192.168.1.127:7789;
meta-disk internal;
}
}
drbd.conf explained:
Global section, usage-count. The DRBD project keeps statistics about the usage of DRBD versions. They do this by contacting a HTTP server each time a new DRBD version is installed on a system. This can be disabled by setting usage-count no;.
The common seciton contains configurations inhereted by all resources defined.
Setting the syncronisation rate, this is accoimplished by going to the syncer section and then assigning a value to the rate setting. The syncronisation rate refers to rate in which the data is being mirrored in the background. The best setting for the syncronsation rate is related to the speed of the network with which the DRBD systems are communicating on. 100Mbps ethernet supports around 12MBps, Giggabit ethernet somewhere around 125MBps.
in the configuration above, we have a resource defined as r0, the nodes are configured in the "on" host subsections.
"Device" configures the path of the logical block device that will be created by DRBD
"Disk" configures the block device that will be used to store the data.
"Address" configures the IP address and port number of the host that will hold this DRBD device.
"Meta-disk" configures the location where the metadata about the DRBD device will be stored.
You can set this to internal and DRBD will use the physical block device to store the information, by recording the metadata within the last sections of the disk.
Once you have created your configuration file, you must conduct the following steps on both the nodes.
Create device metadata.
$ drbdadm create-md r0
v08 Magic number not found
Writing meta data...
initialising activity log
NOT initialized bitmap
New drbd meta data block sucessfully created.
success
Attach the backing device.
$ drbdadm attach r0
Set the syncronisation parameters.
$ drbdadm syncer r0
Connect it to the peer.
$ drbdadm connect r0
Run the service.
$ service drbd start
Heartbeat:
Heartbeat provides the IP redundancy and the service HA functionailty.
On the failure of the primary node the VIP is assigned to the secondary node and the services configured to be HA are started on the secondary node.
Heartbeat configuration:
/etc/ha/ha.conf
## /etc/ha.d/ha.cf on node1
## This configuration is to be the same on both machines
## This example is made for version 2, comment out crm if using version 1
// replace the node variables with the names of your nodes.
crm no
keepalive 1
deadtime 5
warntime 3
initdead 20
bcast eth0
auto_failback yes
node bailey
node giskard
/etc/ha.d/authkeys
// The configuration below set authentication off, and encryption off for the authentication of nodes and their packets.
//Note make sure the authkeys file has the correct permisisions chmod 600
## /etc/ha.d/authkeys
auth 1
1 crc
/etc/ha.d/haresources
//192.168.1.40 is the VIP (Virtual IP) assigned to the cluster.
//the "smb" in the configuration line represents the service we wish to make HA
// /devdrbd0 represents the resource name you configured in the drbd.conf
## /etc/ha.d/haresources
## This configuration is to be the same on both nodes
bailey 192.168.1.40 drbddisk Filesystem::/dev/drbd0::/drbdData::ext3 smb
We are pleased to announce the release of Recital 10.0.2.
Here is a brief list of features and functionality that you will find in the 10.0.2 release.
- New commands
SAVE/RESTORE DATASESSION [TO variable]
CONNECT "connectString"
DISCONNECT - New functions (OData compatible)
startsWith(haystack as character, needle as character)
endsWith(haystack as character, needle as character)
indexOf(haystack as character, needle as character)
substringOf(haystack as character, needle as character)
concat(expC1, expC2) - New system variables
_LASTINSERTEDSYNCNUM - Enhanced commands
Added CONNSTRING "connectingString" to the USE command to connect to remote servers (Recital, MySQL, PostgreSQL, Oracle, ODBC) - Further SQL query optimizer improvements to boost performance
- Performance improvements in Recital Web
- Forced all temporary files into temp directory (improves performance when local tmpfs is used as temp directory and reduces network i/o)
- Fixed cookie and session variable problems in Recital Web
- Fixed problem with temporary files being left after some server queries involving memos and object data types
- Improved performance of the Windows ODBC driver
- Fixed a security flaw in Recital Web
- Fixed all reported bugs
Recital is a rich and versatile product with many ways to do the same thing. Developers usually write code in the way that they are accustomed to without paying much attention to how this will perform in a multi-user environment with large amounts of users and transactions. The best way to optimize Recital applications is to use the built-in tuning capabilities introduced in Recital 10.
In this article Chris Mavin, explains and details how to use the Recital Database Server with the Open Source Servlet Container Apache Tomcat.
Overview
PHP has exploded on the Internet, but its not the only way to create web applications and dynamic websites. Using Java Servlets, JavaServer Pages and Apache Tomcat you can develop web applications in a more powerful full featured Object Oriented Language, that is easier to debug, maintain, and improve.
Tomcat Installation
There are a number of popular Java application servers such as IBM Web Sphere and BEA WebLogic but today we will be talking about the use of Apache Tomcat 5, the Open Source implementation of the Java Servlet and JavaServer Pages technologies developed at the Apache Software Foundation. The Tomcat Servlet engine is the official reference implementation for both the Servlet and JSP specifications, which are developed by Sun under the Java Community Process. What this means is that the Tomcat Server implements the Servlet and JSP specifications as well or better than most commercial application servers.
Apache Tomcat is available for free but offers many of the same features that commercially available Web application containers boast.
Tomcat 5 supports the latest Servlet and JSP specifications, Servlet 2.4, and JSP 2.0, along with features such as:
-
Tomcat can run as a standalone webserver or a Servlet/JSP engine for other Web Servers.
-
Multiple connectors - for enabling multiple protocol handlers to access the same Servlet engine.
-
JNDI - The Java Naming and Domain Interface is supported.
-
Realms - Databases of usernames and passwords that identify valid users of a web application.
-
Virtual hosts - a single server can host applications for multiple domain names. You need to edit server.xml to configure virtual hosts.
-
Valve chains.
-
JDBC - Tomcat can be configured to use any JDBC driver.
-
DBCP - Tomcat can use the Apache commons DBCP for connection pooling.
-
Servlet reloading (Tomcat monitors any changes to the classes deployed within that web server.)
-
HTTP functionality - Tomcat functions as a fully featured Web Server.
-
JMX, JSP and Struts-based administration.
Tomcat Installation
In this next two sections we will walk through the install and setup of Tomcat for use with the Recital database server.
To download Tomcat visit the Apache Tomcat web site is at http://jakarta.apache.org/tomcat.
Follow the download links to the binary for the hardware and operating system you require.
For Tomcat to function fully you need a full Java Development Kit (JDK). If you intend to simply run pre compiled JavaServer pages you can do so using just the Java Runtime Environment(JRE).
The JDK 1.5 is the preferred Java install to work with Tomcat 5, although it is possible to run Tomcat 5 with JDK 1.4 but you will have to download and install the compat archive available from the Tomcat website.
For the purpose of this article we will be downloading and using Tomcat 5 for Linux and JDK 5.0,
you can download the JDK at http://java.sun.com/javase/downloads/index.jsp.
Now we have the JDK, if the JAVA_HOME environment variable isn't set we need to set it to refer to the base JDK install directory.
Linux/Unix:
$ JAVA_HOME= /usr/lib/j2se/1.4/ $ EXPORT $JAVA_HOME
Windows NT/2000/XP:
Follow the following steps:
1. Open Control Panel.
2. Click the System icon.
3. Go to the Advanced tab.
4. Click the Environment Variables button.
5. Add the JAVA_HOME variable into the system environment variables.
The directory structure of a Tomcat installation comprises of the following:
/bin - Contains startup, shutdown and other scripts. /common - Common classes that the container and web applications can use. /conf - Contains Tomcat XML configuration files XML files. /logs - Serlvet container and application logs. /server - Classes used only by the Container. /shared - Classes shared by all web application. /webapps - Directory containing the web applications. /work - Temporary directory for files and directories.
The important files that you should know about are the following:
-
server.xml
The Tomcat Server main configuration file is the [tomcat install path]\conf\server.xml file. This file is mostly setup correctly for general use. It is within this file where you specify the port you wish to be running the server on. Later in this article I show you how to change the default port used from 8080 to port 80.
-
web.xml
The web.xml file provides the configuration for your web applications. There are two locations where the web.xml file is used,
web-inf\web.xml provides individual web application configurations and [tomcat install path]conf\web.xml contains the server wide configuration.
Setting up Tomcat for use
We'll start by changing the port that Tomcat will be listening on to 80.
To do this we need to edit [tomcat install path]/conf/server.xml and change the port attribute of the connector element from 8080 to 80.
After you have made the alteration the entry should read as:
<!-- Define a non-SSL HTTP/1.1 Connector on port 8080 --> <Connector port="80" maxHttpHeaderSize="8192"
Next we want to turn on Servlet reloading, this will cause the web application to be recompiled each time it is accessed, allowing us to make changes to the files without having to worry about if the page is being recompiled or not.
To enable this you need to edit [tomcat install path]/conf/context.xml and change <Context> element to <Context reloadable="true">.
After you have made the alteration the entry should read as:
<Context reloadable="true"> <WatchedResource>WEB-INF/web.xml</WatchedResource> </Context>
Next we want to enable the invoker Servlet.
The "invoker" Servlet executes anonymous Servlet classes that have not been defined in a web.xml file. Traditionally, this Servlet is mapped to the URL pattern "/servlet/*", but you can map it to other patterns as well. The extra path info portion of such a request must be the fully qualified class name of a Java class that implements Servlet, or the Servlet name of an existing Servlet definition.
To enable the invoker Servlet you need to edit the to [tomcat install path]/conf/web.xml and uncomment the Servlet and Servlet-mapping elements that map the invoker /servlet/*.
After you have made the alteration the entry should read as:
<servlet> <servlet-name>invoker</servlet-name> <servlet-class>org.apache.catalina.servlets.InvokerServlet</servlet-class> <init-param> <param-name>debug</param-name> <param-value>0</param-value> </init-param> <load-on-startup>2</load-on-startup> </servlet> <servlet-mapping> <servlet-name>invoker</servlet-name> <url-pattern>/servlet/*</url-pattern> </servlet-mapping>
If you are you not interested in setting up your own install of Tomcat there are prebuilt versions Tomcat that has all of the above changes already made, and has the test HTML, JSP, and Servlet files already bundled. Just unzip the file, set your JAVA_HOME
Next we will give Tomcat and your web applications access to the Recital JDBC driver.
For the purposes of this article we are going to install the Recital JDBC driver in the /[tomcat install path]/common/lib/ this gives Tomcat and your web applications access to the Recital JDBC driver. The driver can be installed in a number of places in the Tomcat tree, giving access to the driver to specific application or just to the web application and not the container. For more information refer to the Tomcat documentation.
Copy the recitalJDBC.jar which is located at /[recital install path]/drivers/recitalJDBC.jar to the /[tomcat install path]/common/lib/ directory.
Linux:
$cp /[recital install path]/drivers/recitalJDBC.jar /[tomcat install path]/common/lib/
Once you have completed all the steps detailed above, fire up the server using the script used by your platform's Tomcat installation.
Linux/Unix:
[tomcat install path]/bin/startup.sh
Windows:
[tomcat install path]/bin/startup
If you are having problems configuring your Tomcat Installation or would like more detail visit the online documentation a the Apache Tomcat site.
Example and Links
Now we have setup our Tomcat installation, lets get down to it with a JSP example which uses the Recital JDBC driver to access the demonstration database (southwind) shipped with the Recital Database Server.
The example provided below is a basic JDBC web application, where the user simply selects a supplier from the listbox and requests the products supplied by that supplier.
To run the example download and extract the tar archive or simple save each of the two jsp pages individually into /[tomcat install path]/webapps/ROOT/ on your server.
By enabling the invoker Servlet earlier we have removed the need to set the example up as a web application in the Tomcat configuration files.
You can now access the example web application at http://[Server Name]/supplier.jsp if the page doesn't display, check you have followed all the Tomcat installation steps detailed earlier in this article and then make sure both Tomcat and a licensed Recital UAS are running.
Downloads:
Archive: jspExample.tar
Right click and save as individual files and rename as .jsp files:
supplier.txt details.txt
Further Reading on JSP and JDBC can be found at http://www-128.ibm.com/developerworks/java/library/j-webdata/
Final Thoughts
Recital and Apache tomcat are a powerful combination, using Java Servlet technology you can separate application logic and the presentation extremely well. Tomcat, JSP, Java Servlets and the Recital database server form a robust platform independent, easily maintained and administered solution with which to unlock the power of your Recital, Foxpro, Foxbase, Clipper, RMS and C-SAM data.
If you have a live linux site that is running vmware virtual machines, you can pause the virtual machines when you want to perform a backup, I use acronis for linux which does incremental backups and you can specify a command to run before and after the backup, this allows backups to be performed at scheduled times daily without any intervention. In my examples below, the virtual machine i want to control is in /root/vmware/Recital/Recital.vmx
To pause the virtual machine on linux:
# vmrun pause /root/vmware/Recital/Recital.vmx
and then to unpause after the backup has completed:
# vmrun unpause /root/vmware/Recital/Recital.vmx
That is basicallty it, no need to attend the backup and it can be perfomed at a suitable time so no users are affected.
Incidentally, vmrun lets you startup a virtual machine at system startup too, without needing the GUI:
# vmrun start /root/vmware/Recital/Recital.vmx
Or alternatively stop it:
# vmrun stop /root/vmware/Recital/Recital.vmx
There are lots of other capabilities of this command, running applications inside the virtual machine etc etc. For full details just type vmrun in a terminal window.
Recital is a dynamic programming language with an embedded high performance database engine particularly well suited for the development and deployment of high transaction throughput applications.
The Recital database engine is not a standalone process with which the application program communicates. Instead, the Recital database is an integral part of any applications developed in Recital.
Recital implements most of the SQL-99 standard for SQL, but also provides lower level navigational data access for performing high transaction throughput. It is the choice of the application developer whether to use SQL, navigational data access, or a combination of both depending upon the type of application being developed.
The Recital database engine, although operating as an embedded database in the user process, multiple users and other background processes may access the same data concurrently. Read accesses are satisfied in parallel. Recital uses automatic record level locking when performing database updates. This provides for a high degree of database concurrency and superior application performance and differentiates the Recital database from other embeddable databases such as sqlite that locks the entire database file during writing.
Key features of the Recital scripting language include:
- High performance database application scripting language
- Modern object-oriented language features
- Easy to learn, easy to use
- Fast, just-in-time compiled
- Loosely-typed
- Garbage collected
- Static arrays, Associative arrays and objects
- Develop desktop or web applications
- Cross-platform support
- Extensive built-in functions
- Superb built-in SQL command integration
- Navigational data access for the most demanding applications
- Scripting language is upward compatible with FoxPRO
Key features of the Recital database include:
- A broad subset of ANSI SQL 99, as well as extensions
- Cross-platform support
- Stored procedures
- Triggers
- Cursors
- Updatable Views
- System Tables
- Query caching
- Sub-SELECTs (i.e. nested SELECTs)
- Embedded database library
- Fault tolerant clustering support
- Chronological data versioning with database timelines
- Optional DES3 encrypted data
- Hot backup
- Client drivers for ODBC, JDBC and .NET