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PRTG Manual: HTTP Sensor

The HTTP sensor monitors a web server using HTTP.

You can use this sensor to monitor if a website or a specific website element is reachable.

HTTP Sensor

For a detailed list and descriptions of the channels that this sensor can show, see section Channel List.

Sensor in Other Languages

Dutch: HTTP
French: HTTP
German: HTTP
Japanese: HTTP
Portuguese: HTTP
Russian: HTTP
Simplified Chinese: HTTP
Spanish: HTTP

Remarks

Consider the following remarks and requirements for this sensor:

Remark	Description
SRP ciphers	This sensor does not support Secure Remote Password (SRP) ciphers.
Smart URL replacement	This sensor supports smart URL replacement.
IPv6	This sensor supports IPv6.
Performance impact	This sensor has a low performance impact.
Knowledge Base	Knowledge Base: My HTTP sensors fail to monitor websites which use SNI. What can I do? Knowledge Base: Which HTTP status code leads to which HTTP sensor status?

Basic Sensor Settings

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

httpsensor

For more information about basic sensor settings, see section Sensor Settings.

HTTP Specific

Setting	Description
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.
URL	Enter the URL that the sensor connects to. If you enter an absolute URL, the sensor uses this address independently of the IP Address/DNS Name setting of the parent device. You can enter the URL of a web page (to measure the loading time of the page's source code), or enter the URL of an image or of a page asset to measure this element's availability and loading time. The URL must be URL encoded. If you monitor an image or a page asset, this can create a high amount of memory load. We recommend that the size of the elements that you want to monitor does not exceed 200 MB. 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.
Request Method	Select an HTTP request method to determine how the sensor requests the URL: GET (default): Directly request the website. We recommend that you use this setting for a simple check of the web page. POST: Send post form data to the URL. If you select this setting, you must enter the data in the Postdata field below. If a POST request is redirected, all further requests are GET (default) requests. HEAD: Only request the HTTP header from the server without the actual web page. Although this saves bandwidth because it transfers less data, we do not recommended that you use this. This is because the measured request time is not the one that your users experience and you might not be notified of slow results or timeouts.
Postdata	This setting is only visible if you select POST above. Enter the data part for the POST request. No Extensible Markup Language (XML) is allowed here.
Content Type	This setting is only visible if you select POST above. Define the content type of the POST request: Default (application/x-www-form-urlencoded): Use the default content type to encode the form data set for submission to the server. Custom: Use a custom content type. Enter the content type below.
Custom Content Type	This setting is only visible if you select Custom above. Define the custom content type, for example, XML, JavaScript Object Notation (JSON), or HTTP.
Server Name Indication	The Server Name Indication (SNI) that the sensor automatically determines from the host address of the parent device or from the target URL of the sensor. The SNI must be a fully qualified domain name (FQDN). Make sure that it matches the configuration of the target server. For more information, see the Knowledge Base: My HTTP sensors fail to monitor websites which use SNI. What can I do? This sensor implicitly supports SNI, an extension to the Transport Layer Security (TLS) protocol.
SNI Inheritance	Define if you want to inherit the SNI from the parent device: Inherit SNI from parent device: Determine the SNI from the host address of the parent device. Do not inherit SNI from parent device: Determine the SNI from the target URL as defined in the settings of this sensor.

Sensor Display

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: 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.

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:

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.

Inherited Settings

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.

Smart URL Replacement

Instead of entering a complete address in the URL field of an HTTP sensor, you can only enter the protocol followed by a colon and three forward slashes (this means that you can enter either http:/// or https:///, or even a simple forward slash / as the equivalent for http:///). PRTG automatically fills in the parent device's IP Address/DNS Name in front of the third forward slash.

Whether this results in a valid URL or not depends on the IP address or Domain Name System (DNS) name of the parent device. In combination with cloning devices, you can use smart URL replacement to create many similar devices.

For example, if you create a device with the DNS name www.example.com and you add an HTTP sensor to it, you can provide values in the following ways:

If you enter https:/// in the URL field, PRTG automatically creates the URL https://www.example.com/
If you enter /help in the URL field, PRTG automatically creates and monitor the URL http://www.example.com/help
It is also possible to provide a port number in the URL field. It is taken over by the device's DNS name and is internally added, for example, http://:8080/

Smart URL replacement does not work for sensors that run on the probe device.

Channel List

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
Loading Time	The web page or element loading time This channel is the primary channel by default.

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

Loading Time

The web page or element loading time

This channel is the primary channel by default.

KNOWLEDGE BASE