<%NUMBERING1%>.<%NUMBERING2%>.<%NUMBERING3%> PRTG Manual: HTTP Advanced Sensor

The HTTP Advanced sensor monitors the source code of a web page using HTTP. It supports authentication, content checks, and other advanced parameters.

The sensor can show the following:

  • Loading time
  • Bytes received
  • Download bandwidth (speed)
  • Time to first byte

icon-i-roundThe monitored content size is uncompressed.

HTTP Advanced Sensor

HTTP Advanced Sensor

Sensor in Other Languages

Dutch: HTTP Geavanceerd, French: HTTP (avancé), German: HTTP (Erweitert), Japanese: HTTP アドバンスト, Portuguese: HTTP avançado, Russian: HTTP (Расширенный), Simplified Chinese: HTTP 高级, Spanish: HTTP Avanzado

Remarks

Add Sensor

The Add Sensor dialog appears when you manually add a new sensor to a device. It only shows the setting fields that are required for creating the sensor. Therefore, you do not see all setting fields in this dialog. You can change (nearly) all settings in the sensor's Settings tab later.

Sensor Settings

On the details page of a sensor, click the Settings tab to change its settings.

icon-i-roundUsually, a sensor connects to the IP Address or DNS Name of the parent device on which you created the sensor. See the Device Settings for details. For some sensors, you can explicitly define the monitoring target in the sensor settings. See below for details on available settings.

Basic Sensor Settings

Sensor Name

Enter a meaningful 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.

Parent Tags

Shows Tags that this sensor inherits from its parent device, group, and probe. This setting is shown for your information only and cannot be changed here.

Tags

Enter one or more Tags, separated by spaces or commas. You can use tags to group sensors and use tag–filtered views later on. Tags are not case sensitive. We recommend that you use the default value.

There are default tags that are automatically predefined in a sensor's settings when you add a sensor. See section Default Tags below.

You can add additional tags to the sensor if you like. Other tags are automatically inherited from objects further up in the device tree. These are visible above as Parent Tags.

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

Priority

Select a priority for the sensor. This setting determines where the sensor is placed in sensor lists. A sensor with a top priority is at the top of a list. Choose from one star (low priority) to five stars (top priority).

Default Tags

httpsensor

HTTP Specific

Timeout (Sec.)

Enter a timeout in seconds for the request. If the reply takes longer than this value, the sensor cancels the request and shows a corresponding error message. Enter an integer value. The maximum value is 900 seconds (15 minutes).

URL

Enter the URL that the sensor connects to. It has to be URL encoded. If you enter an absolute URL, the sensor uses this address independently from 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 another page asset to measure this element's availability and loading time.

icon-i-round-redMonitoring an image or another page asset 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.

icon-i-roundPRTG uses a smart URL replacement that lets you use the parent device's IP address/DNS name setting as part of the URL. For more information, see section Smart URL Replacement below.

Request Method

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

  • GET: Directly request the website, like browsing the web. 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 that is sent in the Postdata field below.
  • HEAD: Only request the HTTP header from the server without the actual web page. Although this saves bandwidth because less data is transferred, it is not recommended because the measured request time is not the one experienced by your users and you might not be notified of slow results or timeouts.

Postdata

This field is only visible if you enable POST above. Enter the data part for the POST request.

icon-i-round-redNo Extensible Markup Language (XML) is allowed here!

Content Type

This field is only visible if you enable POST above. Define the content type of a 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: If you need a custom content type, enter the content type below.

Custom Content Type

This field is only visible if you enable Custom above. Define the custom content type, for example, XML, JavaScript Object Notation (JSON), or HTTP.

Server Name Indication

Shows the Server Name Identification (SNI) that the sensor automatically determined from the host address of the parent device or the target URL of the sensor. The SNI has to be a fully qualified domain name (FQDN). Make sure that it matches the configuration of the target server.

icon-book-bulbFor details, see the Knowledge Base: My HTTP sensors fail to monitor websites which use SNI. What can I do?

SNI Inheritance

Define if you want to inherit the SNI from the parent device:

  • Inherit SNI from parent device: The sensor determines the SNI from the host address of the parent device.
  • Do not inherit SNI from parent device: The sensor determines the SNI from the target URL as defined in the settings of this sensor.

HTTP Engine

Monitoring Engine

If you encounter unexpected errors with the standard method that is used to monitor a URL, try the compatibility mode, which is based on .NET. Choose between:

  • Default/High Performance (recommended): This is the default monitoring method for this sensor.
  • Alternate/Compatibility Mode: Try this method as an alternative for websites that do not work with the default approach. Using the compatibility mode, this sensor executes an external executable program. Because of this, this method needs more resources but it can be helpful in some cases.
    icon-i-roundIf you select the compatibility mode, the options for the SSL method are slightly different. You can also check for trusted certificates. See below.
    icon-i-redWhen using the compatibility mode, Smart URL Replacement does not work, so this sensor does not automatically use the IP Address/DNS value of the parent device.

SSL Specific (when using Compatibility Mode)

SSL Method

When using the compatibility mode, the Secure Sockets Layer (SSL) specific settings are a bit different from the default (automatically used) SSL settings. You can choose from:

  • SSL 3.0
  • TLS 1.0, TLS 1.1, TLS 1.2
  • SSL 3.0, TLS 1.0, TLS 1.1, TLS 1.2: This is the default setting.

Check SSL Certificates

Specify if the sensor checks the certificate of the URL:

  • Do not check used certificates: Do not check the certificates of the web pages. This the default setting.
  • Check if the used certificates are trusted: Check the certificates of the web pages. If the certificate of the server is not trusted, the sensor shows a Down status and displays a corresponding message.

icon-i-roundThis sensor implicitly supports SNI, an extension to the Transport Layer Security (TLS) protocol.

Advanced Sensor Data

Protocol Version

Define the HTTP protocol version that the sensor uses when connecting to the target URL:

  • HTTP 1.0
  • HTTP 1.1: This is the default setting.

User Agent

Choose which user agent string the sensor sends when connecting to the target URL:n:

  • Use the default string: Do not enter a specific user agent and use the default setting. Usually, this is: Mozilla/5.0 (compatible; PRTG Network Monitor (www.paessler.com); Windows).
  • Use a custom string: Use a custom user agent. Define below.

Custom User Agent

This field is only visible if you enable Use a custom string above. Enter the string to be used as the user agent when connecting to the target URL.

HTTP Headers

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

  • Do not use custom HTTP headers: Do not use custom HTTP headers.
  • Use custom HTTP headers: Use custom headers. Define below.

Custom HTTP Headers

This field is only visible if you enable Use custom HTTP headers above. Enter a list of custom HTTP headers and values that you want to transmit to the URL, each pair in one line. The syntax of a header-value pair is header1:value1

icon-i-redThe sensor does not support the header field names user-agent, content-length, and host.

icon-i-redEnsure that the HTTP header statement is valid. Otherwise, the sensor request cannot be successful.

Content Changes

Define what the sensor does if the content of the monitored web page (element) changes:

  • Ignore changes: No action is taken on change.
  • Trigger 'change' notification: The sensor sends an internal message that indicates that the web page content has changed. In combination with a Change Trigger, you can use this mechanism to trigger a notification whenever the web page content changes.

Require Keyword

Define if the sensor checks the result at the configured URL for keywords:

  • Do not check for keyword (default): Do not search for keywords in the result returned at the URL.
  • Set sensor to warning if keyword is missing: Check if a keyword exists in the result. If it exists, set the sensor to a Warning status.
  • Set sensor to error if keyword is missing: Check if a keyword exists in the result. If it exists, set the sensor to a Down status.

icon-i-blueThe content check is only intended for HTML websites and might not work with other target URLs. For example, binary files are not supported.

Response Must Include

This field is only visible if you enable keyword checking above (include). Define which string must be part of the source code at the specified URL. You can enter plain text or a Regular Expression.

If the data does not include the search pattern, the sensor shows the status defined above. Enter a string.

Search Method

Define the format of the search expression:

  • String search (default): Search for the string as plain text. The characters * and ? work here as placeholders, whereas * stands for no number or any number of characters and ? stands for exactly one character (as known from Windows search). This behavior cannot be disabled, so the literal search for these characters is not possible with plain text search. You can also search for HTML tags.
  • Regular expression: Use the search pattern as a Regular Expression.

icon-i-bluePRTG supports Perl Compatible Regular Expression (PCRE) regex. You cannot use regex options or flags. For more details, see section Regular Expressions.

Exclude Keyword

Define if the sensor checks the result at the configured URL for keywords:

  • Do not check for keyword (default): Do not search for keywords in the result returned at the URL.
  • Set sensor to warning if keyword is found: Check if a keyword exists in the result. If it exists, set the sensor to a Warning status.
  • Set sensor to error if keyword is found: Check if a keyword exists in the result. If it exists, set the sensor to a Down status.

icon-i-blueThe content check is only intended for HTML websites and might not work with other target URLs. For example, binary files are not supported.

Response Must Not include

This field is only visible if you enable keyword checking (exclude) above. Define which string must not be part of the source code at the specified URL. You can either enter plain text or a Regular Expression. If the data does include this string, the sensor shows the status defined above. Enter a string.

Search Method

Define the format of the search expression:

  • String search (default): Search for the string as plain text. The characters * and ? work here as placeholders, whereas * stands for no number or any number of characters and ? stands for exactly one character (as known from Windows search). This behavior cannot be disabled, so the literal search for these characters is not possible with plain text search. You can also search for HTML tags.
  • Regular expression: Use the search pattern as a Regular Expression.

icon-i-bluePRTG supports Perl Compatible Regular Expression (PCRE) regex. You cannot use regex options or flags. For more details, see section Regular Expressions.

Download Limit (KB)

Enter the maximum amount of data (in kilobytes) that is transferred per request.

icon-i-round-redIf you set content checks, be aware that they may be incomplete because only the content downloaded up to this limit is checked for search expressions.

Result Handling

Define what the sensor does with the data loaded at the URL:

  • Discard HTML result: Do not store the requested data.
  • Store latest HTML result: Store the last result of the requested data to the Logs (Sensors) directory in the PRTG data folder on the probe system the sensor is running on (on the Master node if in a cluster). File name: Result of Sensor [ID].txt. This is for debugging purposes, especially in combination with content checks. The file is overwritten with each scanning interval.
    icon-book-arrowsFor information on how to find the folder used for storage, see section Data Storage.

icon-prtg-on-demandThis option is not available when the sensor runs on the Hosted Probe of a PRTG hosted by Paessler instance.

icon-i-round-redThis sensor loads the source code at the URL. If you set up a content check, only this source code is checked for the keywords. The code is not necessarily identical to the code used to display the page when opening the same URL in a web browser. This is because a reload may be configured or certain information may be inserted after loading, for example, via JavaScript.

icon-i-round-redPRTG does not follow links to embedded objects nor does it execute scripts. Only the first page at the URL is loaded and checked against the expressions configured.

icon-i-roundFor debugging, use the Result Handling option to write the source code file to disk and to look up what exactly PRTG gets when it calls the URL. If the URL does not point to a web page but to a binary file, for example, to an image, you usually do not check for content.

Authentication

Authentication

Define if authentication is necessary on the web page at the configured URL:

  • No authentication needed
  • Web page needs authentication

User

This field is only visible if you enable Web page needs authentication above. Enter a username. Enter a string.

Password

This field is only visible if you enable Web page needs authentication above. Enter a password. Enter a string.

Authentication Method

This field is only visible if you enable Web page needs authentication above. Select the authentication method that the URL is protected with:

  • Basic access authentication (HTTP): Use simple HTTP authentication. This is the default setting and is suitable for most cases.
    icon-i-round-redThis authentication method transmits credentials as plain text.
  • Windows NT LAN Manager (NTLM): Use the Microsoft NT LAN Manager (NTLM) protocol for authentication. This is sometimes used in intranets for single sign on (SSO).
  • Digest Access Authentication: Use digest access authentication. This applies a hash function to the password, which is safer than basic access authentication.

We recommend that you use the default value.

Sensor Display

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.

icon-i-roundYou can set a different primary channel later by clicking the pin symbol of a channel 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.
    icon-i-roundThis option cannot be used in combination with manual Vertical Axis Scaling (available in the Sensor Channel Settings settings).

Stack Unit

This field is only visible if you enable Stack channels on top of each other above. 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.

Inherited Settings

By default, all of the following settings are inherited from objects that are higher in the hierarchy and should be changed there if necessary. Often, best practice is to change them centrally in the Root group's settings. For more information, see section Inheritance of Settings. To change a setting for this object only, disable inheritance by clicking the button next to inherit from under the corresponding setting name. You then see the options described below.

Proxy Settings for HTTP Sensors

Click inherited_settings_button to interrupt the inheritance. See section Inheritance of Settings for more information.

The proxy settings determine how a sensor connects to a URL. You can enter data for an HTTP proxy server that sensors use when connecting via HTTP or HTTPS.

icon-i-roundThis setting only affects monitoring and it determines the behavior of HTTP sensors. To change proxy settings for the core server, see section System Administration—Core & Probes.

icon-i-roundThe SSL Certificate sensor and the SSL Security Check sensor do not support HTTP proxies but you can configure connections via SOCKS proxies in the sensors' settings.

Name

Enter the IP address or Domain Name System (DNS) name of the proxy server. If you leave this field empty, no proxy is used.

Port

Enter the port number of the proxy. Often, port 8080 is used. Enter an integer value.

User

If the proxy requires authentication, enter the username for the proxy login.

icon-i-round-redOnly basic authentication is available. Enter a string or leave the field empty.

Password

If the proxy requires authentication, enter the password for the proxy login.

icon-i-round-redOnly basic authentication is available. Enter a string or leave the field empty.

Scanning Interval

Click inherited_settings_button to interrupt the inheritance. See section Inheritance of Settings for more information.

Scanning Interval

Select a scanning interval (seconds, minutes, or hours). The scanning interval determines the amount of time that the sensor waits between two scans. You can change the available intervals in the system administration on PRTG on premises installations.

If a Sensor Query Fails

Define the number of scanning intervals that the sensor has time to reach and check a device again in case a sensor query fails. Depending on the option that you select, the sensor can try to reach and check a device again several times before the sensor shows a Down status. This can avoid false alarms if the monitored device only has temporary issues. For previous scanning intervals with failed requests, the sensor shows a Warning status. Choose from:

  • Set sensor to down immediately: Set the sensor to a Down status immediately after the first failed request.
  • Set sensor to warning for 1 interval, then set to down (recommended): Set the sensor to a Warning status after the first failed request. If the following request also fails, the sensor shows an error.
  • Set sensor to warning for 2 intervals, then set to down: Set the sensor to a Down status only after three consecutively failed requests.
  • Set sensor to warning for 3 intervals, then set to down: Set the sensor to a Down status only after four consecutively failed requests.
  • Set sensor to warning for 4 intervals, then set to down: Set the sensor to a Down status only after five consecutively failed requests.
  • Set sensor to warning for 5 intervals, then set to down: Set the sensor to a Down status only after six consecutively failed requests.

icon-i-roundSensors that monitor via Windows Management Instrumentation (WMI) always wait at least one scanning interval before they show a Down status. It is not possible to immediately set a WMI sensor to a Down status, so the first option does not apply to these sensors. All other options can apply.

icon-i-roundIf you define error limits for a sensor's channels, the sensor immediately shows a Down status. No "wait" option applies.

icon-i-roundIf a channel uses lookup values, the sensor immediately shows a Down status. No "wait" options apply.

Schedules, Dependencies, and Maintenance Window

icon-i-roundYou cannot interrupt the inheritance for schedules, dependencies, and maintenance windows. The corresponding settings from the parent objects are always active. However, you can define additional settings here. They are active at the same time as the parent objects' settings.

Schedule

Select a schedule from the list. Schedules can be used to monitor for a certain time span (days or hours) every week.

icon-book-arrowsYou can create schedules, edit schedules, or pause monitoring for a specific time span. For more information, see section Account Settings—Schedules.

icon-i-roundSchedules are generally inherited. New schedules are added to existing schedules, so all schedules are active at the same time.

Maintenance Window

Specify if you want to set up a one-time maintenance window. During a maintenance window, the current object and all child objects are not monitored. They are in a Paused status instead. Choose between:

  • Not set (monitor continuously): No maintenance window is set and monitoring is always active.
  • Set up a one-time maintenance window: Pause monitoring within a maintenance window. You can define a time span for a monitoring pause below and change it even for a currently running maintenance window.

icon-i-roundTo terminate a current maintenance window before the defined end date, change the time entry in Maintenance Ends to a date in the past.

Maintenance Begins

This field is only visible if you enable Set up a one-time maintenance window above. Use the date time picker to enter the start date and time of the maintenance window.

Maintenance Ends

This field is only visible if you enable Set up a one-time maintenance window above. Use the date time picker to enter the end date and time of the maintenance window.

Dependency Type

Define a dependency type. You can use dependencies to pause monitoring for an object depending on the status of another object. You can choose from:

  • Use parent: Use the dependency type of the parent object.
  • Select a sensor: Use the dependency type of the parent object. Additionally, pause the current object if another specific sensor is in a Down status or in a Paused status caused by another dependency.
  • Master sensor for parent: Make this sensor the master object for its parent device. The sensor influences the behavior of its parent device: If the sensor is in a Down status, the device is paused. For example, it is a good idea to make a Ping sensor the master object for its parent device to pause monitoring for all other sensors on the device in case the device cannot even be pinged. Additionally, the sensor is paused if the parent group is paused by another dependency.

icon-i-roundTo test your dependencies, select Simulate Error Status from the context menu of an object that other objects depend on. A few seconds later, all dependent objects are paused. You can check all dependencies under Devices | Dependencies in the main menu bar.

Dependency

This field is only visible if you enable Select a sensor above. Click the Search button and use the object selector to select a sensor on which the current object will depend.

Dependency Delay (Sec.)

This field is only visible if you enable Select a sensor above. Define a time span in seconds for dependency delay.

After the master sensor for this dependency comes back to an Up status, monitoring of the dependent objects is additionally delayed by the defined time span. This can help avoid false alarms, for example, after a server restart, by giving systems more time for all services to start up. Enter an integer value.

icon-i-round-redThis setting is not available if you set this sensor to Use parent or to be the Master sensor for parent. In this case, define delays in the parent Device Settings or in its parent Group Settings.

Access Rights

Click inherited_settings_button to interrupt the inheritance. See section Inheritance of Settings for more information.

User Group Access

Define the user groups that have access to the selected object. A table with user groups and types of access rights is shown. It contains all user groups from your setup. For each user group, you can choose from the following access rights:

  • Inherited: Use the access rights settings of the parent object.
  • None: Users in this group cannot see or edit the object. The object neither shows up in lists nor in the device tree. Exception: If a child object is visible to the user, the object is visible in the device tree but it cannot be accessed.
  • Read: Users in this group can see the object and review its monitoring results.
  • Write: Users in this group can see the object, review its monitoring results, and edit its settings. They cannot edit access rights settings.
  • Full: Users in this group can see the object, review its monitoring results, edit its settings, and edit access rights settings.

You can create new user groups in the System Administration—User Groups settings. To automatically set all objects further down in the hierarchy to inherit this object's access rights, set a check mark for the Revert children's access rights to inherited option.

icon-book-arrowsFor more details on access rights, see section User Access Rights.

Channel Unit Configuration

Click inherited_settings_button to interrupt the inheritance. See section Inheritance of Settings for more information.

Channel Unit Types

For each type of sensor channel, define the unit in which data is displayed. If defined on probe, group, or device level, these settings can be inherited to all sensors underneath. You can set units for the following channel types (if available):

  • Bandwidth
  • Memory
  • Disk
  • File
  • Custom

icon-i-roundCustom channel types can be set on sensor level only.

Smart URL Replacement

Instead of entering a complete address in the URL field of an HTTP sensor, you can simply 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 or 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, smart URL replacement makes it easy 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/

icon-i-round-redSmart URL replacement does not work for sensors that run on the probe device.

More

Knowledge Base: Which HTTP status code leads to which HTTP sensor status?

Knowledge Base: Which user agent should I use in the HTTP Advanced sensor's settings?

Knowledge Base: My HTTP sensors fail to monitor websites which use SNI. What can I do?

Knowledge Base: Why do my HTTP Advanced sensors differ in the bytes received value?

Knowledge Base: My HTTP sensors don't work. What can I do?

Edit Sensor Channels

To change display settings, spike filtering, and limits, switch to the sensor's Overview tab and click the gear icon of a specific channel. For detailed information, see section Sensor Channel Settings.

Notification Triggers

Click the Notification Triggers tab to change notification triggers. For detailed information, see section Sensor Notification Triggers Settings.

Others

For more general information about settings, see section Object Settings.

Sensor Settings Overview

For information about sensor settings, see the following sections:

Keywords: