Testing Database Connectivity

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  • When troubleshooting a new environment, it is often helpful to isolate the various components in play and test them in isolation as simply as possible.

    For testing connectivity to a database, a simple TCP connection can be made by using the telnet application. The advantage of using telnet is that is extremely simple. There are no configuration files to modify and no authentication. It either makes the connection or does not.

    Once you know that the database is accessible, you can move on to testing via applications such as your database’s native client, or Looker.

    Installing Telnet

    Some hosts may come with Telnet pre-installed. To test this, try:

    telnet ?
    

    You should see something like this:

    usage: telnet [-l user] [-a] [-s src_addr] host-name [port]
    

    If you get a “command not found” error you will need to install telnet.

    On Ubuntu:

    sudo apt-get install telnet
    

    On Redhat/CentOS:

    yum install telnet
    

    Default Ports

    You will need to know which port your database is running on. The following table lists the default ports for a number of platforms, although your database may be configured to run on a different port. Consult your database administrator.

    Platform Port
    Amazon Redshift 5439
    GreenPlum 5432
    Microsoft SQL Server (MSSQL) 1433
    MySQL 3306
    Oracle 1521
    PostgreSQL 5432
    Vertica 5433

    Connecting to Your Database with Telnet

    To test the connection to your database, run telnet hostname port. For example, if you are running MySQL on the default port and your database name is mydb, the command would be telnet mydb 3306.

    If the connection is working, you will see something similar to this:

    Trying 10.10.10.10...
    Connected to mydb.
    Escape character is '^]'.
    

    If the connection is NOT working, you will see something like one of these:

    Trying 10.10.10.10...
    telnet: Unable to connect to remote host: Connection timed out
    
    Trying 127.0.0.1...
    telnet: Unable to connect to remote host: Connection refused
    
    telnet: could not resolve mydb/telnet: Name or service not known
    

    Troubleshooting

    If the telent check is not successful, consider the following:

    • Is the hostname correct?
    • Are the db and telnet hosts configured to allow the network traffic between them? Check any installed firewall software on both hosts.
    • Are all the networks between the telnet and database hosts configured to allow the network traffic? Check firewalls and network Access Control Lists (ACLs).
    • Are all the networks between the telnet and database hosts configured correctly to route traffic between the hosts?
    • Is the database server running, is it listening on the correct port, and is it configured to allow connections from the telnet server?

    Next Steps

    If you are able to telnet your your database server’s port you can rule out basic connectivity issues. The next step is to create a Looker database connection.

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