Webcron
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webcron is the term for a time-based
Overview
Many web hosts offer shell accounts or some sort of built-in job scheduler such as cron that makes it easy for users to schedule jobs. Such hosts run jobs as
A webcron solution is made up of two pieces. The first piece is a script that will execute the tasks that resides somewhere accessible via a URL. The second piece is to use a scheduling provider that contacts the URL of the script at regular intervals.
Before setting up a schedule with a scheduling provider, a user must set up a script that runs on the web server. Most[
Scheduling Providers
Third-Party
There are many third-party webcron scheduling providers on the web.
Users who set up premium accounts on third-party webcron scheduling providers typically[
Some webcron service providers accept
Visitor Based
A webcron solution can be contained entirely on a web host by letting visitors trigger a webcron scheduler script on the server. For instance, this can be accomplished by using an
If there are insufficient visitors to a website using visitor based webcron scheduling, then scheduled tasks will not run on time.
Since visitor based webcron scheduling enables the possibility of self-contained webcron solutions, it increases the portability of a website or web-based software product. Some web-based open-source software that have tasks that need to run regularly use a visitor based webcron solution to execute those tasks.[citation needed]
Remote Access
A remote access capable webcron solution is typically[peacock prose] bundled with a pair of client and server components. The client runs on a separate computer, such as the user's personal computer. A job schedule is set up on the computer where the client component resides. Then, when the job runs, the client component communicates with the server component.[1][non-primary source needed]
Remote access usually[peacock prose] offers capabilities that are impossible with other scheduling providers. The data between the client and server components is typically[peacock prose] encrypted even across HTTP. This allows a plugin or module for the client component to talk to the server component to securely request information that is normally[peacock prose] restricted.[1] Compression of the data sent and received helps reduce overall bandwidth used.[9][non-primary source needed]
A typical[peacock prose] implementation of a remote access plugin or module is to incrementally back up files and databases from the web server to the client. Some incremental backup implementations may even offer basic host-based intrusion detection system functionality.[9]
Local Access
A webcron solution can be used on hosts that already have cron available. This is useful[peacock prose] when required functionality is only available via the web server. The cron daemon is the scheduling provider and periodically contacts the script using another tool such as Wget.
In the case of a remote access capable webcron solution, cron can run the client component to execute the script.
Security Concerns
Since webcron solutions involve availability via a URL, there are several different security concerns that users should address. A webcron solution introduces issues of trust, opportunities for
When using a third-party scheduling provider, users trust the third-party to not misuse the URL in any way. Users also have to assume that the connection between the third-party server and the web server is secure from hackers.
When using a visitor based scheduling provider, users may inadvertently provide a possible venue for denial-of-service attacks. Also, if a script is written improperly, the script may unintentionally expose information about the server.
When using a remote access scheduling provider, users usually[peacock prose] have refined control over how communication takes place with the web server. If HTTP is used, the URL is sent in the clear over the wire but the data in the request is typically[peacock prose] encrypted. This opens up the possibility of denial-of-service attacks and replay attacks.
References
- ^ a b c d e WebCron product documentation, retrieved December 1, 2010
- ^ a b phpJobScheduler overview documentation, retrieved October 14, 2010
- ^ SetCron is a task scheduler service/ webcron that allows you to schedule cronjobs.
- ^ Webcron services
- ^ a b EasyCron plans
- ^ SetCronJob premium pricing page, retrieved October 14, 2010
- ^ EasyCron accepts cron expression
- ^ What are the crontab features of SetCron?
- ^ a b WebCron Site Backup module documentation, retrieved December 1, 2010