# 32. Configuration File Shortcuts

This appendix describes features that AMPS provides for simplifying configuration.

## AMPS Configuration File Special Characters

In AMPS there are a few special characters that you should be aware of when creating your configuration file. These characters can provide some handy shortcuts and make configuration creation easier, but you should also be aware of them so as not to introduce errors.

### State of the World File Name

When specifying the file for a State of the World database, using the `%n` string in the file name specifies that the AMPS server will use the message type and topic name in that position to create a unique file name. The example below shows how to use this in the AMPS configuration file.

    <SOW>
        <Topic>
            <Topic>Customers</Topic>
            <FileName>./sow/%n.sow</FileName>
            <MessageType>json</MessageType>
            <Key>/customerId</Key>
        </Topic>
    </SOW>

SOW file name tokens used in configuration file

### Log Rotation Name

When specifying an AMPS log file which has `RotationThreshold` specified, using the `%n` string in the log file name is a useful mechanism for ensuring the name of the log file is unique and sequential. The example below shows a file name token replacement in the AMPS configuration file.

    <Logging>
        <Target>
            <Protocol>file</Protocol>
            <Level>info</Level>
            <FileName>log/log-%n.log</FileName>
            <RotationThreshold>2G</RotationThreshold>
        </Target>
    </Logging>

Log file name used in configuration file

In the above example, a log file will be created in the `AMPSDIR/log/` directory. The first time this file is created, it will be named `log-1.log`. Once the log file reaches the `RotationThreshold` limit of 2G, the previous log file will be saved, and the new log file name will be incremented by one. Thus, the next log file will be named `AMPSDIR/log/log-2.log`.

### Dates

AMPS allows administrators to use date based file names when specifying the file name in the configuration, as demonstrated in the example below.

    <Logging>
        <Target>
            <Protocol>file</Protocol>
            <Level>info</Level>
            <FileName>
                log/log-%Y-%m-%dT%H%M%S.log
            </FileName>
            <RotationThreshold>2G</RotationThreshold>
        </Target>
    </Logging>

Date tokens used in configuration file

In the above example, a log file will be created in the `$AMPSDIR/log` named `2011-01-01-120000.log` if the log was created at noon on January 1, 2011.

AMPS provides full support for the date tokens provided by the standard strftime function, with the exception of `%n`, as described above. The following table shows some of the most commonly used tokens:

Commonly Used Date and Time Tokens
Token | Description | Example
--- | --- | ---
%a | Short weekday name | Fri
%A | Full weekday name | Friday
%b | Short month name | Feb
%B | Full month name | February
%c | Simple date and time | Fri Feb 14 17:25:00 2014
%C | Century | 20
%d | Day of the month (leading zero if necessary) | 05
%D | Short date format (MM/DD/YY) | 02/20/14
%e | Day of the month (leading space if necessary) | 5
%F | Short date format (YYYY-MM-DD) | 2014-02-20
%H | Hour (00-23) | 17
%I | Hour (00-12) | 05
%j | Day of the year (001-366) | 051
%m | Month (01-12) | 02
%p | AM or PM | PM
%r | Current time, 12 hour format | 05:25:00 pm
%R | Current time, 24 hour format | 17:25
%T | ISO 8601 Time format | 17:25:00
%u | ISO 8601 day of the week (1-7, Monday = 1) | 5
%V | ISO 8601 week number (00-53) | 07
%y | Year, last two digits | 14
%Y | Year, four digits | 2014
%Z | Timezone name or abbreviation (blank if undetermined) | PST

## Using Units in the Configuration

To make configuration easy, AMPS permits the use of units to expand values. For example, if a time interval is measured in seconds, then the letter `s` can be appended to the value. For example, the following SOW topic definition uses the `Expiration` tag to set the record expiration to 86400 seconds (one day).

    <SOW>
        <Topic>
            ...

            <Expiration>86400s</Expiration>

            ...
        </Topic>
    </SOW>

Expiration using seconds

An even easier way to specify an expiration of one day is to use the following `Expiration`:

    <SOW>
        <Topic>
            ...

            <Expiration>1d</Expiration>

            ...
        </Topic>
    </SOW>

Expiration using days

The table below shows a listing of the time units AMPS supports in the configuration file.

AMPS Configuration - Time Units
Units | Description
--- | ---
`ns` | nanoseconds
`us` | microseconds
`ms` | milliseconds
`s` | seconds
`m` | minutes
`h` | hours
`d` | days
`w` | weeks

AMPS configuration supports a similar mechanism for byte-based units when specifying sizes in the configuration file. The table below shows a listing of the byte units AMPS supports in the configuration file.

AMPS Configuration - Byte Units
Units | Description
--- | ---
`kb` | kilobytes
`mb` | megabytes
`gb` | gigabytes
`tb` | terabytes

Dealing with large numbers in AMPS configuration can also be simplified by using common exponent values to handle raw values. This means that instead of having to input `10000000` to represent ten million, a user can input `10M`. The table below contains a list of the exponents supported.

AMPS Configuration - Numeric Units
Units | Description
--- | ---
k | 103 - thousand
M | 106 - million

Tip

To make it easier for users to remember the units, AMPS interval and byte units are not case sensitive.

## Environment Variables in AMPS Configuration

AMPS configuration also allows for environment variables to be used as part of the data when specifying a configuration file. These variables can be set in the environment when AMPS starts, or passed to AMPS using the `-D` option on the command line.

If a global system variable is commonly used in an organization, then it may be useful to define this in one location and re-use it across multiple AMPS installations or applications. AMPS will replace any token wrapped in `${}` with the environment variable defined in the current user operating system environment. The example below demonstrates how the environment variable `ENV_LOG` is used to define a global environment variable for the location of the host logging.

    <Logging>
        <Target>
            <Protocol>file</Protocol>
            <FileName>${ENV_LOG}</FileName>
            <Level>info</Level>
            <RotationThreshold>2G</RotationThreshold>
        </Target>
    </Logging>

Environment variables in AMPS configuration

## Internal Environment Variables

In addition to supporting custom environment variables, AMPS includes a set of environment variables automatically populated by the server.

These variables are listed below:

Variable Name | Contains
--- | ---
`AMPS_CONFIG_DIRECTORY` | Directory in which the configuration file used to start AMPS is located.
`AMPS_CONFIG_PATH` | Full path to the configuration file used to start AMPS, including the file name.
`AMPS_VERSION` | Full version number of the AMPS server.

When AMPS processes the configuration file, AMPS expands these variables just as though they were set in the environment. For example, assume that AMPS was started with the following command at the command prompt:

    %>./ampServer ../amps/config/config.xml

Given this command, the log file configuration option shown in the example below can be used to instruct AMPS to create the log files in the same parent directory as the configuration file — in this case `../amps/config/logs/infoLog.log`.

    <Logging>
        <Target>
            <Protocol>file</Protocol>
            <FileName>${AMPS_CONFIG_DIRECTORY}/logs/infoLog.log</FileName>
            <Level>info</Level>
            <RotationThreshold>2G</RotationThreshold>
        </Target>
    </Logging>

AMPS_CONFIG_DIRECTORY environment variable example