PRTG Manual: REST Custom v2 Sensor

Enabled Beta Sensors experimental feature

This sensor requires that the Beta Sensors experimental feature of PRTG is enabled.

For more information, see the Knowledge Base: What are beta sensors and how can I use them?

Channel #2 - #10

You can define up to 10 channels. You must define at least one data channel, so you see all available settings for Channel #1. Specify how to handle all other possible channels:

• Disable: Do not create this channel.
• Enable: Create this channel.

It is not possible to enable or disable channels after sensor creation.

Channel #x JSONPath/XPath

Enter the JSONPath or XPath of the JSON or XML result that you want to monitor.

JSONPath example:

$.store.book[0].year

XPath example:

/store/book[1]/year

Channel #x Name

Enter a name for the channel. Enter a string. For example, Total.

If the name contains angle brackets (<>), PRTG replaces them with braces ({}) for security reasons. For more information, see the Knowledge Base: What security features does PRTG include?

Channel #x Unit

Enter the unit for the value that this sensor monitors. For example, #.

You can change this value later in the channel settings of this sensor.

Sensor Name

Enter a name to identify the sensor. By default, PRTG shows this name in the device tree, as well as in alarms, logs, notifications, reports, maps, libraries, and tickets.

If the name contains angle brackets (<>), PRTG replaces them with braces ({}) for security reasons. For more information, see the Knowledge Base: What security features does PRTG include?

Parent Tags

The tags that the sensor inherits from its parent device, parent group, and parent probe.

This setting is for your information only. You cannot change it.

Tags

Enter one or more tags. Confirm each tag with the Spacebar key, a comma, or the Enter key. You can use tags to group objects and use tag-filtered views later on. Tags are not case-sensitive. Tags are automatically inherited.

It is not possible to enter tags with a leading plus (+) or minus (-) sign, nor tags with parentheses (()) or angle brackets (<>).

For performance reasons, it can take some minutes until you can filter for new tags that you added.

The sensor has the following default tags that are automatically predefined in the sensor's settings when you add the sensor:

• rest

Priority

Select a priority for the sensor. This setting determines the position of the sensor in lists. The highest priority is at the top of a list. Choose from the lowest priority () to the highest priority ().

Request URL

Enter the URL of the JSON or XML REST API endpoint that you want to request.

Example URL:

https://:1616/api/health?token=%restbearertoken&name=%restusername&refresh=true

You can use the following placeholders in this field: %restusername, %restpassword, %restbearertoken, %restplaceholder1, %restplaceholder2, %restplaceholder3, %restplaceholder4, and %restplaceholder5. You can define these placeholders in the credentials for REST API in settings that are higher in the object hierarchy.

PRTG uses a smart URL replacement with which you can use the parent device's IP address or Domain Name System (DNS) name setting as part of the URL. For more information, see section Smart URL Replacement.

If you enter 127.0.0.1 as IP address of the parent device, PRTG requests the following URL:

https://127.0.0.1:1616/api/health?token=%restbearertoken&name=%restusername&refresh=true

Request Method

Select the HTTP request method that the sensor uses to request the REST API:

• GET (default): Use the GET method to request the REST API.
• POST: Use the POST method to request the REST API.

POST Body

This setting is only visible if you select POST above. Enter the data part for the POST request.

You can use the following placeholders in this field: %restusername, %restpassword, %restbearertoken, %restplaceholder1, %restplaceholder2, %restplaceholder3, %restplaceholder4, and %restplaceholder5. You can define these placeholders in the credentials for REST API in settings that are higher in the object hierarchy.

Custom Headers

Enter a list of custom HTTP headers with their respective values that you want to transmit to the target URL. The syntax of a header-value pair is header1:value1.

Custom header example:

host:host1.example.com
User-Agent:PRTG sensor 0.1
X-API-Key: %restplaceholder1

If you enter more than one header-value pair, enter each pair in one line:
header1:value1
header2:value2
header3:value3

Make sure that the HTTP header statement is valid. Otherwise, the sensor request cannot be successful.

You can use the following placeholders in this field: %restusername, %restpassword, %restbearertoken, %restplaceholder1, %restplaceholder2, %restplaceholder3, %restplaceholder4, and %restplaceholder5. You can define these placeholders in the credentials for REST API in settings that are higher in the object hierarchy.

Timeout (Sec.)

Enter a timeout in seconds for the request. Enter an integer. The maximum timeout value is 900 seconds (15 minutes).

If the reply takes longer than this value, the sensor cancels the request and shows a corresponding error message.

Content Type

Select the type of the content that the sensor queries. Choose between:

• JSON (default)
• XML

Custom Sensor Message

Enter the JSONPath or XPath from which you want to receive a string that the sensor shows as the permanent sensor message.

JSONPath example:

$.store.book[0].title

XPath example:

/store/book[1]/title

Channel #x JSONPath/XPath

Enter the JSONPath or XPath of the JSON or XML result that you want to monitor.

JSONPath example:

$.store.book[0].year

XPath example:

/store/book[1]/year

Channel #x Name

Enter a name for the channel.. Enter a string. For example, Total. PRTG dynamically generates channels with this name as the identifier.

If the name contains angle brackets (<>), PRTG replaces them with braces ({}) for security reasons. For more information, see the Knowledge Base: What security features does PRTG include?

Channel #x Value Type

Select the value type that the channel displays:

• Absolute (integer): Integer64 values with or without an operational sign, such as 10 or 120 or -12 or 120.
• Absolute (float): Double values, such as -5.80 or 8.23.
  If you select Absolute (float), the sensor automatically shows all decimal places of the received value in the channel. You can define how many decimal places of the channel's data that you want to display in graphs and tables in the channel settings.
• Delta (counter): Counter values. The sensor calculates the difference between the last and the current value. Enter an integer. The sensor additionally divides the delta value by a time period to indicate a speed value.

This mode only works if the difference between the last and the current value is positive and increases with each scanning interval. This mode does not support negative values and decreasing values.

• Status (string): The sensor shows a status depending on how you map the returned strings and shows the returned strings as sensor message.
• Lookup: The sensors shows a status depending on how you define values in a custom lookup file.

Absolute (integer) and Absolute (float) support the extraction of numerical values from a received string. The sensor parses the numerical value from the beginning of the string until it encounters the first element that is not part of a numerical value, for example a letter. The sensor ignores whitespace characters.

You cannot change this value after sensor creation.

Channel #x Unit

This setting is only visible if you select Absolute (integer), Absolute (float), or Delta (counter) as Channel #x Value Type. Choose between:

• Custom (default)
• Percent
• Percent (CPU)
• Temperature (celsius)
• Time (milliseconds)
• Time (hours)
• Time (seconds)
• Bytes (memory)
• Bytes (disk)
• Bytes (file)
• Bytes (bandwidth)
• Bytes per second (disk)
• Bytes per second (network)

You cannot change this value after sensor creation.

Channel #x Custom Unit

This setting is only visible if you select Custom (default) as Channel #x Unit. Enter the custom unit of the value of this channel. Enter a string.

Channel #x Strings mapped to the 'Up' status

This setting is only visible if you select Status (string) as Channel #x Value Type. Enter the strings that the sensor maps to the Up status in a comma-separated list.

If a string contains a comma, you must put the string in quotation marks. For example, to map the string Friday,2nd enter "Friday,2nd". If a string contains quotation marks, you must escape the quotation marks using a backslash (\) and put the string in quotation marks. For example, to map the string Friday "2nd" enter "Friday \"2nd\"".

Channel #x Strings mapped to the 'Warning' status

This setting is only visible if you select Status (string) as Channel #x Value Type. Enter the strings that the sensor maps to the Warning status in a comma-separated list.

If a string contains a comma, you must put the string in quotation marks. For example, to map the string Friday,2nd enter "Friday,2nd". If a string contains quotation marks, you must escape the quotation marks using a backslash (\) and put the string in quotation marks. For example, to map the string Friday "2nd" enter "Friday \"2nd\"".

Channel #x Strings mapped to the 'Down' status

This setting is only visible if you select Status (string) as Channel #x Value Type. Enter the strings that the sensor maps to the Down status in a comma-separated list.

If a string contains a comma, you must put the string in quotation marks. For example, to map the string Friday,2nd enter "Friday,2nd". If a string contains quotation marks, you must escape the quotation marks using a backslash (\) and put the string in quotation marks. For example, to map the string Friday "2nd" enter "Friday \"2nd\"".

Channel #x Unmapped String Mapping

This setting is only visible if you select Status (string) as Channel #x Value Type. Select the status to which the sensor maps all remaining strings in the returned result that are not manually mapped to the Up, the Warning, and the Down status. Choose between:

• 'Up' status: Map all unknown strings to the Up status.
• 'Warning' status: Map all unknown strings to the Warning status.
• 'Down' status (default): Map all unknown strings to the Down status.

Channel #x Lookup ID

This setting is only visible if you select Lookup as Channel #x Value Type. Enter the ID of the lookup you wish to use. You can find the ID in the ValueLookup parameter in the lookup file.

For more information, see section Define Lookups.

You cannot change this value after sensor creation.

Channel #2 - #10

You can define up to 10 channels. You must define at least one data channel, so you see all available settings for Channel #1. Specify how to handle all other possible channels:

• Disable: Do not create this channel.
• Enable: Create this channel.

It is not possible to enable or disable channels after sensor creation.

Primary Channel

Select a channel from the list to define it as the primary channel. In the device tree, the last value of the primary channel is always displayed below the sensor's name. The available options depend on what channels are available for this sensor.

You can set a different primary channel later by clicking below a channel gauge on the sensor's Overview tab.

Graph Type

Define how different channels are shown for this sensor:

• Show channels independently (default): Show a graph for each channel.
• Stack channels on top of each other: Stack channels on top of each other to create a multi-channel graph. This generates a graph that visualizes the different components of your total traffic.
  You cannot use this option in combination with manual Vertical Axis Scaling (available in the channel settings).

Stack Unit

This setting is only visible if you enable Stack channels on top of each other as Graph Type. Select a unit from the list. All channels with this unit are stacked on top of each other. By default, you cannot exclude single channels from stacking if they use the selected unit. However, there is an advanced procedure to do so.

Result Handling

Define what PRTG does with the sensor result:

• Discard result: Do not store the sensor result.

• Store result: Store the last sensor result in the \Logs\sensors subfolder of the PRTG data directory on the probe system. The file name is Result of Sensor [ID].log. This setting is for debugging purposes. PRTG overwrites this file with each scanning interval.

This option is not available when the sensor runs on the hosted probe of a PRTG Hosted Monitor instance.

In a cluster, PRTG stores the result in the PRTG data directory of the master node.

Example

To demonstrate the practical usage of JSONPath, we use this JSON example that a REST query might have returned as reference in this section.

{
"devices":[
 {
   "firmware":{
     "id":"0.7",
     "date":"2017-05-18T17:11:43.7049944Z",
     "channel": "beta"
   },
   "networks": {
     "a": {
       "rx_bytes": 35985021,
       "rx_packets": 176791,
       "rx_errors": 0,
       "rx_dropped": 476,
       "tx_bytes": 7229493,
       "tx_packets": 35518,
       "tx_errors": 0,
       "tx_dropped": 1
     },
     "b": {
       "rx_bytes": 40085321,
       "tx_bytes": 55294975
     }
   }
 },
 {
   "networks": {
     "a": {
       "rx_bytes": 63685865,
       "tx_bytes": 7229472
     }
   }
 }
 ]
}

Root

The dollar sign ($) matches the root element of the JSON data.

Child

You can match a child with .<key> or [<key>]

• .<key> must only contain letters, numbers, and underscore (_). Hyphens (-) must be escaped with quotation marks.
• [<key>] must only contain a number or a quoted string.

Example

This expression matches 35985021 in the example above:

$.devices.0.networks.a.rx_bytes

You get the same result with this expression:

$["devices"][0]["networks"]["a"]["rx_bytes"]

If an element contains a hyphen (-), the .<key> notation does not work. Use the [<key>] notation in this case:

$["data"][0]["system-stats"]["temps"]["Board (CPU)"]

Wildcard

To match multiple values, you can use the asterisk symbol (*).

• .*
• [*]

Example

This expression matches 35985021 and 40085321 in the example above:

$.devices[0].networks.*.rx_bytes

Recursive Descent

You can match all subitems of a node with two dots (..).

Example

This expression matches 7229493 and 55294975 and 7229472 in the example above:

$..tx_bytes

Union

You can match multiple children with [<key1>,<key2>,<...>].

Example

This expression matches 35985021 and 7229493 in the example above:

$.devices.0.networks.a["rx_bytes","tx_bytes"]

Slice

You can match multiple children of an array with [<begin>:<end>] or [<begin>:<end>:<step>].

• By default, begin, end, and step are either integers or empty.
• The default approach is to go step by step from the first array element to the last element.
• Step can also be a negative integer to go through the array in reversed order.

Example

This expression matches 63685865 and 7229472 in the example above:

$.devices[-1:].networks.a[rx_bytes,tx_bytes]

Current

The @ symbol matches the current element.

Example

This expression matches 63685865 and 7229472 in the example above:

$.devices[(@.length-1)].networks.a.rx_bytes

Filter

You can filter matches with [?<expression>].

Example

This expression matches 35985021 in the example above because the first device is the only one with a beta channel:

$.devices[?(@.firmware.channel=="beta")].networks.a.rx_bytes

Constant

• Numeric constants as 64-bit floating point: 12345.678
• String constants with double quotation marks ("): "switch"
• Boolean constants: true and false
  If the JSONPath points to a boolean, the sensor translates true as 1 and false as 0.

Functions

You can use functions on top level or in filters.

This expression returns the number items in the element devices in the example above:

length($.devices)

For more information about functions, see JsonCons JSONPath | Functions.

Operator

• Parentheses control the order of evaluation: (<expression>)
• Arrays with brackets: [<expression>, <expression>, ...]
• Objects: {<expression>:<expression>, <expression>:<expression>, ...}

Example

To demonstrate the practical usage of XPath, we use this XML example that a REST query might have returned as reference in this section.

<?xml version="1.0" encoding="UTF-8" ?>
<root>
 <devices>
   <firmware>
     <id type="major">0</id>
     <id type="minor">7</id>
     <date>2017-05-18T17:11:43.7049944Z</date>
     <channel>beta</channel>
   </firmware>
   <networks>
     <a>
       <rx_bytes>35985021</rx_bytes>
       <rx_packets>176791</rx_packets>
       <rx_errors>0</rx_errors>
       <rx_dropped>476</rx_dropped>
       <tx_bytes>7229493</tx_bytes>
       <tx_packets>35518</tx_packets>
       <tx_errors>0</tx_errors>
       <tx_dropped>1</tx_dropped>
     </a>
     <b>
       <rx_bytes>40085321</rx_bytes>
       <tx_bytes>55294975</tx_bytes>
     </b>
   </networks>
 </devices>
 <devices>
   <networks>
     <a>
       <rx_bytes>63685865</rx_bytes>
       <tx_bytes>7229472</tx_bytes>
     </a>
   </networks>
 </devices>
</root>

Root

The slash symbol (/) matches the root element of the XML data.

Child

You can match a child by its name with /<key> or [<key>] or by its index with [<index>].

• /<key> must only contain letters, numbers, and underscore (_). Hyphens (-) must be escaped with quotation marks.
• [<key>] must only contain a number or a quoted string.
• [<index>] must only contain a number.

Example

This expression matches 35985021 in the example above:

/root/devices[1]/networks/a/rx_bytes

This expression matches major in the example above:

/root/devices[1]/firmware/id[1]/@type

Wildcard

To match multiple values, you can use the asterisk symbol (*).

• /*
• /@*
• [*]
• [@*]

Example

This expression matches 35985021 and 40085321 in the example above:

/root/devices[1]/networks/*/rx_bytes

Recursive Descent

You can match all subitems of a node with two slashes (//).

Example

This expression matches 7229493 and 55294975 and 7229472 in the example above:

//tx_bytes

Union

You can match multiple queries by combining them with the vertical bar symbol (|).

Example

This expression matches 35985021 and 7229493 in the example above:

/root/devices[1]/networks/a/rx_bytes | /root/devices[1]/networks/a/tx_bytes

Filter

You can filter matches with [<expression>].

Example

This expression matches 35985021 in the example above because the first device is the only one with a beta channel:

/root/devices[firmware/channel='beta']/networks/a/rx_bytes

This expression matches 0 in the example above:

/root/devices[1]/firmware[1]/id[@type='major']

Constant

• Numeric constants as 64-bit floating point: 12345.678
• String constants with double quotation marks ("): "switch"

• Boolean constants: true and false
  If the XPath points to a boolean, the sensor translates true as 1 and false as 0.

Functions

You can use functions on top level or in filters.

This expression returns the number of items in the devices element in the example above:

count(/root/devices[position() < 3])

For more information about functions, see XML Path Language (Core Function Library).

Operator

• Parentheses control the order of evaluation: (<expression>)

Examples

/root/one + /root/two

eval($.root.one + $.root.two)

Addition of the numbers

3

3

n/a

eval($.root.one + to_number($.root.two_string))

Addition of a number and a string

n/a

3

/root/one + /root/two/@value_int

n/a

Addition of a number and an attribute value

3

n/a

/root/four div /root/two

eval($.root.four / $.root.two)

Division of two integers. The expected result is an integer

2

2

/root/one div /root/two

eval($.root.one / $.root.two)

Division of two integers, the expected result is a floating-point number

0.5

0

n/a

eval($.root.one / $.root.two * 1.0)

Division of two integers with a floating point number as result

n/a

0.5

/root/one div /root/two_point5

eval($.root.one / $root.two_point5)

Division of a float and an integer

0.4

0.4

/root/one = /root/two

eval($.root.one == $.root.two)

If entries are equal

0 (false)

0 (false)

Downtime

In the channel table on the Overview tab, this channel never shows any values. PRTG uses this channel in graphs and reports to show the amount of time in which the sensor was in the Down status

HTTP Status

The HTTP status that the requested URL returns

• Up status: Continue, Switching Protocols, Processing, OK, Created, Accepted, Non-Authoritative Information, No Content, Reset Content, Partial Content, Multi-Status, Already Reported, IM Used
• Warning status: Multiple Choices, Moved Permanently, Found, See Other, Not Modified, Use Proxy, Switch Proxy (deprecated), Temporary Redirect, Permanent Redirect,
• Down status: Bad Request, Unauthorized, Payment Required, Forbidden, Not Found, Method Not Allowed, Not Acceptable, Proxy Authentication Required, Request Time-out, Conflict, Gone, Length Required, Precondition Failed, Request Entity Too Large, Request URL Too Long, Unsupported Media Type, Requested Range Not Satisfiable, Expectation Failed, I'm a teapot, Policy Not Fulfilled, There are too many connections from your internet address, Unprocessable Entity, Locked, Failed Dependency, Unordered Collection, Upgrade Required, Precondition Required, Too Many Requests, Request Header Fields Too Large, No Response, The request should be retried after doing the appropriate action, Unavailable For Legal Reasons, Internal Server Error, Not Implemented, Bad Gateway, Service Unavailable, Gateway Time-out, HTTP Version not supported, Variant Also Negotiates[13], Insufficient Storage, Loop Detected, Bandwidth Limit Exceeded, Not Extended
• Unknown status: Unknown

This channel is the primary channel by default.

[Value]

The values that a REST API returns in several channels