How to Check If a Virtual DataPort Server Is Alive¶
When you connect to Denodo through a load balancer or an application that creates a pool of connections to Virtual DataPort, the load balancer or the application need a way to check that a connection is still valid. The following sections explain different alternatives to check the health of a connection.
Using the Ping Script¶
The script ping
checks that a Virtual DataPort server is “alive”. It
is located in the directory <DENODO_HOME>/bin
.
ping [ -t timeout ] [ -r ] [ -q <query> -l <login> [ -p <password> | -cf <configuration file> ] ] [ -v ]
<host>[:<port>][/<database name>
Parameter |
Description |
---|---|
-t |
Optional. Time to wait for a response, in milliseconds. If after this period the script does not receive a response, it returns an error. |
-r |
Optional. Checks when the server is ready for processing queries and not in single user/promotion mode (optional, ignored when using -q). |
-q <query> |
Optional. If present, the script, besides checking if the Virtual DataPort server is up, it executes a query. If you indicate this parameter, you also have to pass the login and password of the user. In many operating systems, you have to surround the query with double quotes so the query is considered a single parameter. |
-l |
Mandatory when using |
-p |
Password. Incompatible with If you provide the login ( If you are going to invoke this from another script of application, we recommend encrypting the password; to avoid putting in plain text. |
-cf <file> |
Incompatible with
or this:
|
-v |
Optional. If present, the script displays the status the time taken to receive a response from the Server. Otherwise, it only displays error messages. |
<host> |
Host of Virtual DataPort. |
<port> |
Optional. If not present, the script sends the request to the default Virtual DataPort port: 9999. |
<database> |
Mandatory when using |
This script returns 1 if there is any error (e.g. the server cannot be reached or the query fails or the timeout is reached…). If the script finishes correctly, it returns 0.
Examples
Example 1
For Windows:
<DENODO_HOME>\bin\ping.bat -v -t 30000 -q "SELECT 1" -l monitor_user -p "encrypted:UjOsIu8972jviqGpcLP3Mg==" //denodo-dv1.acme.com/admin
For Linux:
<DENODO_HOME>/bin/ping.sh -v -t 30000 -q "SELECT 1" -l monitor_user -p "encrypted:UjOsIu8972jviqGpcLP3Mg==" //denodo-dv1.acme.com/admin
This sends a ping request to “denodo-dv1.acme.com”:
If the server responds, it executes the query “SELECT 1” on the database “admin”. Note that the query (
-q
parameter) needs to be surrounded by double quotes so the query is considered a single parameter.If connecting to Virtual DataPort and running the query takes more than 30 seconds, the script fails.
Note that the password (parameter
-p
) starts withencrypted:
. That is because what follows is the password encrypted.
To encrypt the password of a user account, execute this:
On Windows:
<DENODO_HOME>\bin\encrypt_password.bat
On Linux:
<DENODO_HOME>/bin/encrypt_password.sh
Enter your password and press Enter; the script will return your password encrypted. You can also pass your password as a parameter of this script.
Example 2
ping -t 30000 -v //denodo-dv1.acme.com:19999
Sends a ping request to a Virtual DataPort that listens on the port 19999, with a timeout of 30 seconds. Unlike in the previous example, this one does not execute any query. That is why you do not need to specify the user and password.
Alternatives to the Ping Script¶
In an environment where the load balancer cannot run a ping query, nor use the ping script, you can develop a script that sends an HTTP request to Virtual DataPort through the RESTful Web service.
It is important for the queried view to be very lightweight. We suggest creating this view with this statement:
CREATE OR REPLACE VIEW ping_query_view AS
SELECT 1;
When this view is queried, it only invokes the internal stored procedure
Dual
and does not involve any data source.
Then, develop a script that access the URL
http://denodo-dv1.acme.com:9090/denodo-restfulws/admin/views/ping_query_view
This URL will return the HTTP code 200 if Virtual DataPort server is alive.