How to increase max connection in MySql

When you try to make a large number of connections to the MySQL server, sometimes you might get the following error.

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Data source rejected establishment of connection,  message from server: "Too many connections"

There are two values governing the max number of connections one can create

1. max_user_connections
2. global.max_connections

1. max_user_connections

The max_user_connections is a user level parameter which you can set for each user. To let a user to create any number of connections set the above mentioned value to zero '0'.

First view the current  max_user_connections:

SELECT max_user_connections FROM mysql.user WHERE user='my_user' AND host='localhost';

Then set it to zero

GRANT USAGE ON *.* TO my_user@localhost MAX_USER_CONNECTIONS 0;

2. global.max_connections

The global.max_connections is a global parameter and has the precedence over 
max_user_connections. Hence just increasing the max_user_connections is not enough. Hence you have to increase the max_user_connections as well.

set @@global.max_connections = 1500;

Reference:

[1] http://dba.stackexchange.com/questions/47131/how-to-get-rid-of-maximum-user-connections-error

[2] https://www.netadmintools.com/art573.html

Installing and Configuring NGINX in ubuntu (for a Simple Setup)

In this post I am going to present you, how to install NGINX and setup it to operate with simple HTTP routing.

Below are the two easy steps to install NGINX in your ubuntu system.

sudo apt-get update
sudo apt-get install nginx

Once you are done go to any web browser and type in "http://localhost", in case  you are installing in the local machine or "http://[IP_ADDRESS]"

This will show you the default HTTP page hosted by NGINX

Welcome to nginx!

If you see this page, the nginx web server is successfully installed and working. Further configuration is required.

For online documentation and support please refer to nginx.org.
Commercial support is available at nginx.com.

Thank you for using nginx.

Below are few easy commands to "Stop", "Start" or "Restart"

sudo service nginx stop
sudo service nginx start
sudo service nginx restart

By now you have NGINX installed, up and running on your system.

We will next we how to configure NGINX to listen to a particular port and route the traffic to some other end points.

Below is a sample configuration file you need to create. Let's first see what each of these configuration means.

"upstream" : represents a group of endpoints that you need to route you requests.

"upstream/server" : an endpoint that you need to route you requests.

"server" : represent the configurations for listing ports and routing locations

"server/listen" : this is the port that NGINX will listen to

"server/server_name" : the server name this machine (where you install the NGINX)

"server/location/proxy_pass" : the group name of the back end servers you need to route your requests to. 

upstream backends {
    server 192.168.58.118:8280;
    server 192.168.88.118:8280;
}

server {
    listen 8280;
    server_name 192.168.58.123;
    location / {
        proxy_pass http://backends;
    }
}

The above configuration instructs NGINX to route requests that is coming into "192.168.58.123:8280", to be routed into "192.168.58.118:8280" or "192.168.88.119:8280" in round robin manner.

1. To make that happen you have to create a file with above configuration at "/etc/nginx/sites-available/mysite1". You can use any name you want. In this example I named it as "mysite1".

2. Now you have to enable this configuration by creating a symbolic link to the above file in "/etc/nginx/sites-enabled/" location
/etc/nginx/sites-enabled/mysite1 -> /etc/nginx/sites-available/mysite1

3. Now the last step. You have to restart the NGINX to get the new configurations affected.

Once restarted, any request you send to "192.168.58.123:8280" will be load balanced in to "192.168.58.118:8280" or "192.168.88.119:8280" in round robin manner.

Hope this helps you to quickly setup NGINX for you simple routing requirements