# Scheduling a crawler
<a name="schedule-crawler"></a>

You can run an AWS Glue crawler on demand or on a regular schedule. When you set up a crawler based on a schedule, you can specify certain constraints, such as the frequency of the crawler runs, which days of the week it runs, and at what time. You can create these custom schedules in *cron* format. For more information, see [cron](http://en.wikipedia.org/wiki/Cron) in Wikipedia.

When setting up a crawler schedule, you should consider the features and limitations of cron. For example, if you choose to run your crawler on day 31 each month, keep in mind that some months don't have 31 days.

**Topics**
+ [Create a crawler schedule](create-crawler-schedule.md)
+ [Create a schedule for an existing crawler](Update-crawler-schedule.md)

# Create a crawler schedule
<a name="create-crawler-schedule"></a>

You can create a schedule for the crawler using the AWS Glue console or AWS CLI.

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#### [ AWS Management Console ]

1. Sign in to the AWS Management Console, and open the AWS Glue console at [https://console.aws.amazon.com/glue/](https://console.aws.amazon.com/glue\). 

1. Choose **Crawlers** in the navigation pane.

1. Follow steps 1-3 in the [Configuring a crawler](define-crawler.md) section.

1. In [Step 4: Set output and scheduling](define-crawler-set-output-and-scheduling.md), choose a **Crawler schedule** to set the frequency of the run. You can choose the crawler to run hourly, daily, weekly, monthly or define custom schedule using cron expressions.

   A cron expression is a string representing a schedule pattern, consisting of 6 fields separated by spaces: \$1 \$1 \$1 \$1 \$1 <minute> <hour> <day of month> <month> <day of week> <year> 

   For example, to run a task every day at midnight, the cron expression is: 0 0 \$1 \$1 ? \$1

   For more information, see [Cron expressions](https://docs.aws.amazon.com/glue/latest/dg/monitor-data-warehouse-schedule.html#CronExpressions).

1. Review the crawler settings you configured, and create the crawler to run on a schedule.

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#### [ AWS CLI ]

```
aws glue create-crawler 
 --name myCrawler \
 --role AWSGlueServiceRole-myCrawler  \
 --targets '{"S3Targets":[{Path="s3://amzn-s3-demo-bucket/"}]}' \
 --schedule cron(15 12 * * ? *)
```

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For more information about using cron to schedule jobs and crawlers, see [Time-based schedules for jobs and crawlers](monitor-data-warehouse-schedule.md). 

# Create a schedule for an existing crawler
<a name="Update-crawler-schedule"></a>

Follow these steps to set up a recurring schedule for an existing crawler.

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#### [ AWS Management Console ]

1. Sign in to the AWS Management Console and open the AWS Glue console at [https://console.aws.amazon.com/glue/](https://console.aws.amazon.com/glue\). 

1. Choose **Crawlers** in the navigation pane.

1. Choose a crawler that you want to schedule from the available list.

1. Choose **Edit** from the **Actions menu.**

1. Scroll down to **Step 4: Set output and scheduling**, and choose **Edit**. 

1.  Update your crawler schedule under **Crawler schedule**. 

1. Choose **Update**.

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#### [ AWS CLI ]

Use the following CLI command to update an existing crawler configuration:

```
aws glue update-crawler-schedule 
   --crawler-name myCrawler
   --schedule cron(15 12 * * ? *)
```

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