PRTG Manual: REST Custom Sensor
The REST Custom sensor queries a Representational State Transfer (REST) application programming interface (API) endpoint and maps the JavaScript Object Notation (JSON) or Extensible Markup Language (XML) result to sensor values.
The mapping rule must be available as a REST configuration file in JSON template (*.template) format according to the PRTG API definition for custom sensors.
For a detailed list and descriptions of the channels that this sensor can show, see section Channel List.
- Dutch: REST Aangepast
- French: REST personnalisé
- German: REST (Benutzerdef.)
- Japanese: REST カスタム
- Portuguese: REST (customizado)
- Russian: Специальные настройки REST
- Simplified Chinese: REST 自定义
- Spanish: REST (personalizado)
Consider the following remarks and requirements for this sensor:
Remark |
Description |
---|---|
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. |
The sensor has the following default tags that are automatically predefined in the sensor's settings when you add the sensor:
- restcustomsensor
- restsensor
For more information about basic sensor settings, see section Sensor Settings.
Setting |
Description |
---|---|
Request Method |
Select an HTTP request method to determine how the sensor requests 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:
|
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:
|
Authentication Method |
Select the authentication method for access to the REST API:
|
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:
|
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. |
Setting |
Description |
---|---|
Result Handling |
Define what PRTG does with the sensor result:
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. |
Setting |
Description |
---|---|
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:
|
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. |
By default, all of these settings are inherited from objects that are higher in the hierarchy. We recommend that you change them centrally in the root group settings if necessary. To change a setting for this object only, click under the corresponding setting name to disable the inheritance and to display its options.
For more information, see section Inheritance of Settings.
Define Channels and Select Channel Values
In your REST configuration file, you must define which values of the returned JSON or XML are mapped to which channels.
- A channel is defined by the channel key in your REST configuration. See the JSON Return Format: Minimum Example in section Custom Sensors.
- A channel value is defined by an expression that retrieves and processes the value from the JSON source. The expression can contain JSONPath, gval operators, and functions.
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&
This REST query returns some JSON, for example: { 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. { The channel values are the values of the corresponding properties of the REST result defined in JSONPath notation, $.sensorxref[0].totalsens (28) and $.sensorxref[0].downsens (0). Each value's property (destination) and the text property is set to the appropriate transformation rules from source to destination. This is the JSON path of the source. The sensor replaces each path with the value from the source. |
Several REST configuration files are available in the \Custom Sensors\rest subfolder by default. They are ready for use. You can also analyze them to see how to write your own REST configuration.
The REST Custom sensor uses JSONPath to assign values from the returned JSON to channels. With JSONPath, you provide the path to the value in the JSON source that you want to monitor in a channel.
The JSONPath implementation that PRTG uses for the REST Custom sensor might differ from other JSONPath implementations. You can test and debug your definitions using the command line. To test simple JSONPath expressions and calculations, you can also use JSONPath Online Evaluator, for example. Note that this tool might not work properly with complex JSONPath expressions that PRTG supports.
Example To demonstrate the practical usage of JSONPath, we use this JSON example that a REST query might have returned as reference in this section. { |
Root |
The dollar sign ($) matches the root element of the JSON data. |
Child |
You can match a child with .<key> or [<key>].
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>].
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:$.devices[*].channel} This is an extension of the official JSONPath. |
Constant |
|
Operator |
|
Calculating Channel Values and Functions
You can perform calculations with the values of the source JSON or XML. The sensor uses the Paessler gval package for the calculations. For more information, refer to the gval documentation.
The following operators and functions are available to calculate channel values.
|
Operator |
Description |
Operand Type |
Output Type |
Infix Modifiers |
+ |
plus |
number |
number |
- |
minus |
number |
number |
|
* |
times |
number |
number |
|
** |
power of |
number |
number |
|
% |
modulo |
number |
number |
|
/ |
divide |
number |
number |
|
& |
bitwise and |
number |
number |
|
| |
bitwise or |
number |
number |
|
^ |
bitwise xor |
number |
number |
|
<< |
shift left |
number |
number |
|
>> |
shift right |
number |
number |
|
Logical Infix Operators |
> |
greater than |
number/string |
bool |
>= |
equal or greater than |
number/string |
bool |
|
< |
less than |
number/string |
bool |
|
<= |
equal or less than |
number/string |
bool |
|
== |
equal |
any |
bool |
|
!= |
not equal |
any |
bool |
|
=~ |
match regular expression |
string |
bool |
|
!~ |
mismatch regular expression |
string |
bool |
|
in |
contains element |
any, array |
bool |
|
&& |
and |
and |
bool |
|
|| |
or |
or |
bool |
|
?? |
coalescence |
any |
any |
|
Prefix Operators |
- |
negative |
number |
number |
~ |
bitwise not |
number |
number |
|
! |
not |
bool |
bool |
duration(start,end) |
Example duration($.devices[0].firmware.date, "017-05-18T17:11:43.7049944Z") |
now() |
Example duration($.devices[0].firmware.date, now()) |
number(string, [base]) |
Examples number("10.5") |
len(object/array/string) |
Example len($..(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) |
Example sum([1,2,3]) This expression returns 6. |
mean(array-/object-of-numbers) |
Example mean([1,2,3]) This expression returns 2. |
lookup(string, string, string, ...) |
Example lookup($.device[0].firmware.channel, "stable", "beta", "alpha") This expression returns 1 because $.device[0].firmware.channel resolves to beta. |
implode(array-/object-of-string, string) |
Example implode($..tx_bytes, ",") This expression returns 7229493,7229472. |
You can create a template in your REST configuration that defines generic channels. Generic channels are created based on the data that the REST endpoint returns. When the returned value is an array or object, the sensor creates a channel for each element and concatenates the corresponding key to the channel name.
Example
Imagine that you want to have a total byte channel for each network adapter that is defined in the JSON example above. You can do this by creating a dynamic channel like in the following example.
{
"prtg": {
"result":[
{
"value": {
"Total bytes on device" + #0 + " in network " + #1: $.devices.*.networks[*](@.rx_bytes + @.tx_bytes)
},
"CustomUnit": "Bytes"
}
]
}
}
Every channel must have a unique name. You cannot remove channels once they have been added and they keep their last received value. You can add new channels.
If the REST source returns XML instead of JSON, the sensor transforms the XML result to JSON before replacing the value paths with source values. Because of this, you do not know the structure of the source JSON to correctly provide the paths.
In this case, manually execute the sensor executable rest.exe from the \Sensor System subfolder of the PRTG program directory on the probe system. Execute rest.exe with the address of the XML endpoint and the parameter passthrough. The rest executable returns the converted XML to a JSON result that you can use to define the desired paths.
rest.exe <xml-endpoint-url> passthrough
To create a suitable REST configuration for the sensor, you might want to check the returned JSON or XML and see what happens when your mapping rules apply.
The REST Custom sensor is an EXE sensor, so you can test and debug your configuration by executing rest.exe with several parameters. The rest.exe file is located in the \Sensor System subfolder of the PRTG program directory.
The command syntax is as follows:
rest.exe url template|passthrough|channelDiscovery [flags]
rest.exe: Parameters |
|
---|---|
url |
|
template |
|
passthrough |
|
channelDiscovery |
|
rest.exe: Flags |
|
---|---|
-authtoken <string> |
|
-authusername <string> |
|
-authuserpwd <string> |
|
-customheaders <string> |
|
-post=<int> |
Example -customheaders 'Content-Type: application/x-www-form-urlencoded' -post=1 -requestbody 'myvar=value' |
-proxy <string> |
|
-proxyusername <string> |
|
-proxyuserpwd <string> |
|
-requestbody <string> |
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> |
|
-tlsignore=<int> |
|
-template |
|
Which channels the sensor actually shows might depend on the target device, the available components, and the sensor setup.
Channel |
Description |
---|---|
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. |
PRTG MANUAL
KNOWLEDGE BASE
What security features does PRTG include?
Can I create a sensor to monitor the number of paused or unknown sensors?
MISCELLANEOUS
Paessler JSONPath
Paessler Gval
JSONPath Online Evaluator