PRTG Manual: REST Custom Sensor

File storage

The sensor requires that you store the REST configuration file that contains the mapping rules on the probe system. In a cluster, copy the file to every cluster node.

Channels

This sensor does not officially support more than 50 channels. If there are more than 50 channel mappings in the REST configuration file, the sensor shows an error.

IPv6

This sensor supports IPv6.

Performance impact

This sensor has a medium performance impact.

Cluster

In a cluster, status changes triggered by limits only work on the master node.

Hosted probe

You cannot add this sensor to the hosted probe of a PRTG Hosted Monitor instance. If you want to use this sensor, add it to a remote probe device.

Request Method

Select an HTTP request method to determine how the sensor requests the REST API:

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

If you use the POST method, use the content type, for example application/x-www-form-urlencoded, as HTTP header. In section HTTP Headers, select Send custom HTTP headers and enter the content type in the Custom HTTP Headers field.

Postdata

This setting is only visible if you select POST above.

Enter the data part for the POST request.

If you use the POST method, use the content type, for example application/x-www-form-urlencoded, as HTTP header. In section HTTP Headers, select Send custom HTTP headers and enter the content type in the Custom HTTP Headers field.

Request Protocol

Define the security protocol of the HTTP request:

• HTTP (default): Send the REST query via HTTP (not secure).
• HTTPS: Send the REST query via secure HTTPS.

Certificate Acceptance

This setting is only visible if you select HTTPS above.

Select the kind of certificates that you want the sensor to accept for the connection:

• Accept trusted certificates only (default): Accept only trusted certificates issued by a certificate authority (CA).
• Accept all certificates: Accept all certificates, including self-signed certificates.

Authentication Method

Select the authentication method for access to the REST API:

• No authentication (default): Do not use any authentication for the request.
• Basic authentication: Use a user name and password for authentication.
• Basic authentication with Windows credentials from parent device: Use the Windows credentials from the parent device.
  For more information, see section Inheritance of Settings.
• Token: Use a JSON Web Token (JWT) or OAuth2 Bearer Token for authentication.

User Name

This setting is only visible if you select Basic authentication above.

Enter a user name for the REST API. Enter a string.

Password

This setting is only visible if you select Basic authentication above.

Enter a password for the REST API. Enter a string.

Token

This setting is only visible if you select Token above.

Enter a JWT or OAuth2 Bearer Token that the REST API requires for authentication.

HTTP Headers

Define if you want to send custom HTTP headers to the target URL:

• Do not send custom HTTP headers
• Send custom HTTP headers

Custom HTTP Headers

This setting is only visible if you select Send custom HTTP headers above.

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

If you enter more than one header-value pair, you must separate them with delimiters. The syntax is header1:value1|header2:value2|header3:value3

The sensor does not support the header field names user-agent, content-length, host.

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

If you select the POST as Request Method setting above, enter the content type, for example application/x-www-form-urlencoded, as the custom HTTP header.

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.

REST Query

The REST query that this sensor executes. To change it, enter a valid query for the target REST API. The syntax is: [:port]/path[?var1=val1&...]

The sensor always inherits the first part of the address from the address of the parent device. Only enter the path to the REST endpoint of the parent device. You can override the port if necessary.

For example, if you add the sensor to a probe device, a query to the REST API of your PRTG installation that returns the number of sensors on the probe could look like this:

/api/table.json?id=1&passhash=<passhash>&username=<username>&content=sensorxref&noraw=1&filter_basetype=probe&columns=totalsens=textraw

REST Configuration

Select a REST configuration file from the list. The sensor uses it to map the JSON or XML result from the REST query to sensor values.

The default REST configuration file is channelDiscovery. If you select this file, the sensor parses the returned JSON or XML and automatically creates channels based on available values: one channel for each number and boolean for strings if they are convertible into numbers.

This list shows all REST configuration files that are available in the \Custom Sensors\rest subfolder of the PRTG program directory on the probe system. For the files to appear in this list, store the files as JSON template (*.template) in this subfolder.

To use custom REST configurations in PRTG Hosted Monitor, contact the Paessler support team, or add this sensor to a remote probe instead and save the file on the remote probe system.

To show the expected values and sensor status, your files must return the expected JSON format. Channels, values, and messages must be embedded in valid JSON using JSONPath. For more information, see section Define Channels and Select Channel Values.

For more information on how to create custom sensors and for the return format, see section Custom Sensors.

If you use custom sensors on the cluster probe, copy your files to every cluster node.

Result Handling

Define what PRTG does with the sensor result:

• Discard result (default): Do not store the sensor result.
• Store result: Store the sensor result and the last response in the \Logs\sensors subfolder of the PRTG data directory on the probe system. The file names are Result of Sensor [ID].txt and Result of Sensor [ID].Data.txt. This setting is for debugging purposes. PRTG overwrites these files 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.

Primary Channel

Select a channel from the list to define it as the primary channel. In the device tree, PRTG displays the last value of the primary channel 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 this sensor shows different channels:

• 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 select Stack channels on top of each other above.

Select a unit from the list. PRTG stacks all channels with this unit 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.

Example

For this example, we take PRTG as REST endpoint and query the sensor status statistics for the local probe. The REST query that we enter in the sensor settings looks like this:

/api/table.json?id=1&passhash=<passhash>&username=<username>&content=sensorxref&
noraw=1&filter_basetype=probe&columns=totalsens=textraw,upsens=textraw,
downsens=textraw,partialdownsens=textraw,warnsens=textraw,pausedsens=textraw,
unusualsens=textraw,undefinedsens=textraw,downacksens=textraw

This REST query returns some JSON, for example:

   {
   "prtg-version": "17.3.33.2517",
   "treesize": 1,
   "state": "ok",
   "sensorxref": [
     {
       "totalsens": 28,
       "upsens": 18,
       "downsens": 0,
       "partialdownsens": 0,
       "warnsens": 0,
       "pausedsens": 9,
       "unusualsens": 1,
       "undefinedsens": 0,
       "downacksens": 0
     }
   ]
 }

Your REST configuration has to translate this JSON for the sensor. It has to be available as JSON template (*template) in the \Custom Sensors\rest subfolder of the PRTG program directory on the probe system. See section Custom Sensors for details about the JSON return format.

The following example returns two channels from the JSON resource that are added to the sensor in PRTG, Total (total sensor count) and Alarms (sensors in the Down status), each selected by their keys in the returned JSON.

{
   "prtg": {
     "result": [
       {
         "channel": "Total" ,
         "value": $.sensorxref[0].totalsens
       },
       {
         "channel": "Alarms" ,
         "value": $.sensorxref[0].downsens
       }
     ]
   }
 }

The channel values are the values of the corresponding properties of the REST result defined in JSONPath notation, $.sensorxref[0].totalsens (28) and $.sensorxref[0].downsens (0).

Each value's property (destination) and the text property is set to the appropriate transformation rules from source to destination. This is the JSON path of the source. The sensor replaces each path with the value from the source.

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 (-) are not supported.
• [<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 in the example above:

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

Current

The @ symbol matches the current element.

Example

This expression matches 40.085321 and 55.294975 in the example above and can be used to receive a percentage value:

$.devices[1].networks.a.["rx_bytes","tx_bytes"](@/100000000*100)

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[[email protected]=="beta"].networks.a.rx_bytes

Script

You can modify matches with (<expression>) and keys with [<expression>].

Example

This expression matches true and false in the example above because only the first device has a beta channel:

$.devices[*](@.firmware.channel=="beta")

Placeholder

Placeholders give access to values of wildcards in a match. A placeholder #n (where n is a natural number) represents the value of the nth wildcard. You can use this in the keys of JSON arrays.

Example

This expression creates a JSON map from ids to the corresponding firmware channel and matches {"0.7":"beta"} in the example above:

{$.devices[#0].id:$.devices[*].channel}

This is an extension of the official JSONPath.

Constant

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

Operator

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

Operator

Description

Operand Type

Output Type

Infix Modifiers

+

plus

number

number

-

minus

number

number

*

times

number

number

**

power of

number

number

%

modulo

number

number

/

divide

number

number

&

bitwise and

number

number

|

bitwise or

number

number

^

bitwise xor

number

number

<<

shift left

number

number

>>

shift right

number

number

Logical Infix Operators

>

greater than

number/string

bool

>=

equal or greater than

number/string

bool

<

less than

number/string

bool

<=

equal or less than

number/string

bool

==

equal

any

bool

!=

not equal

any

bool

=~

match regular expression

string

bool

!~

mismatch regular expression

string

bool

in

contains element

any, array

bool

&&

and

and

bool

||

or

or

bool

??

coalescence

any

any

Prefix Operators

-

negative

number

number

~

bitwise not

number

number

!

not

bool

bool

duration(start,end)

• Calculates the nanoseconds between start and end.
• Both parameters must be RFC3339 date time strings.

Example

duration($.devices[0].firmware.date, "017-05-18T17:11:43.7049944Z")

now()

• Returns the current date time in RFC3339.

Example

duration($.devices[0].firmware.date, now())

number(string, [base])

• Converts a string to a floating point number.
• If the base is not set, it is detected via the prefix of the string.
  • "0": base = 8
  • "0X": base = 16
  • otherwise: base = 10
  • Decimals are only supported at base 10.

Examples

number("10.5")
number("a", 16)

len(object/array/string)

• Returns the length of an array or string and counts the number of properties in a JSON object.

Example

len($..(number(@)))

This expression counts every number or string that can be converted into a number. It returns 13 in the example above.

sum(array-/object-of-numbers)

• Returns the sum of an array of numbers.

Example

sum([1,2,3])

This expression returns 6.

mean(array-/object-of-numbers)

• Returns the average value of an array of numbers.

Example

mean([1,2,3])

This expression returns 2.

lookup(string, string, string, ...)

• Returns the index of the specified string in a string list, or -1 if the string is not found.

Example

lookup($.device[0].firmware.channel, "stable", "beta", "alpha")

This expression returns 1 because $.device[0].firmware.channel resolves to beta.

implode(array-/object-of-string, string)

• Returns the concatenation of each string in the array, separated by the specified string.

Example

implode($..tx_bytes, ",")

This expression returns 7229493,7229472.

url

• Address of the REST API endpoint that returns JSON or XML

template

• Fully qualified path and file name of your REST configuration file used to map the JSON result to the sensor

passthrough

• No mapping, only returning the queried JSON or XML
• Useful to analyze XML that has been converted to JSON

channelDiscovery

• Creates a channel for every number or boolean in the returned JSON or XML
• If possible, it converts string values to number or boolean values.

-authtoken <string>

• JWT or OAuth2 Bearer Token to send with the request in authorization header as Bearer

-authusername <string>

• User name for basic authentication

-authuserpwd <string>

• User password for basic authentication

-customheaders <string>

• key1:val1|key2:val2|...

-post=<int>

• {1|0}
• Default: 0
• 0 results in a GET request.
• 1 results in a POST request.

Example

-customheaders 'Content-Type: application/x-www-form-urlencoded' -post=1 -requestbody 'myvar=value'

-proxy <string>

• Proxy server connection

-proxyusername <string>

• Proxy user name with basic authentication

-proxyuserpwd <string>

• Proxy user password with basic authentication

-requestbody <string>

• Body of the request

You can only use this flag a POST request (-post=1).

Example

-customheaders 'Content-Type: application/x-www-form-urlencoded' -post=1 -requestbody 'myvar=value'

-timeout <integer>

• Sensor timeout in seconds
• Default: 10

-tlsignore=<int>

• {1|0}
• Default: 0
• 1 accepts self-signed certificates on HTTPS connections

-template

• Returns the discovered template if you use channelDiscovery.

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.

Response Time

The response time

This channel is the primary channel by default.

[Value]

The values that a REST API returns in several channels

For more information about the return value format, see section Custom Sensors.