# Prioritize game session placement
Amazon GameLift Servers uses an algorithm to determine how to prioritize a queue's destinations and determine where to place a new game session. The algorithm is based on an ordered set of criteria. You can use the default priority order, or you can customize the order. You can edit a queue's priority order at any time.
**Default priority order**
1. **Latency** – If the game session placement request includes location-specific latency data for players, Amazon GameLift Servers calculates the average player latency in each location and attempts to place a game session in a fleet location with the lowest average.
1. **Cost** – If a request doesn't include latency data, or if multiple fleets have equal latency, then Amazon GameLift Servers evaluates the hosting cost of each fleet. A fleet's hosting cost varies based on fleet type (Spot or On-Demand), instance type, and location.
1. **Destination** – If multiple fleets have equal latency and costs, then Amazon GameLift Servers prioritizes fleets based on the destination order as listed in the queue configuration.
1. **Location** – For queues with multi-location fleets, if all other criteria are equal, then Amazon GameLift Servers prioritizes the fleet's locations based on alphabetical order.
## Customize how a queue prioritizes game session placements
You can choose to customize how a queue prioritizes the placement criteria. The queue applies the custom prioritization to all game session placement requests that it receives.
**Note**
If you create a custom priority configuration and don't include all four criteria, Amazon GameLift Servers automatically appends any missing criteria in the default order.
**To customize a queue’s priority configuration**
Use the [Amazon GameLift Servers console](https://console.aws.amazon.com/gamelift/) or the AWS Command Line Interface (AWS CLI) to create a custom priority configuration.
------
#### [ Console ]
In the [Amazon GameLift Servers console](https://console.aws.amazon.com/gamelift/), you can customize a queue's priorities when creating a new queue or updating an existing queue. Select an AWS Region to work in.
Open the console’s left navigation bar and choose **Queues**. On the Queues page, select an existing queue and choose **Edit**.
1. Go to the section **Game session placement priority**. Drag and drop each priority criteria to create the order you want.
1. Go to the section **Location order**. Add any locations that you want to prioritize. This list is useful when the queue has fleets with multiple locations. At a minimum, you must specify one location. The locations you specify here are prioritized first, followed by all other locations in the queue's destinations.
1. Choose **Save changes**.
------
#### [ AWS CLI ]
Use the [https://awscli.amazonaws.com/v2/documentation/api/latest/reference/gamelift/update-game-session-queue.html](https://awscli.amazonaws.com/v2/documentation/api/latest/reference/gamelift/update-game-session-queue.html) command with the `--priority-configuration` option to customize a queue's priority order. Amazon GameLift Servers updates a queue in your current default AWS Region, or you can add a `--region` tag to specify a different AWS Region.
The following example request adds or updates the priority configuration for a specified queue
```
aws gamelift update-game-session-queue \
--name "example-queue-with-priority"
--priority-configuration PriorityOrder="COST','LOCATION","DESTINATION",LocationOrder="us-east-1","us-east-2","ca-central-1","us-west-2" \
```
------
## Prioritize placements by player latency
If you want to give your players the best possible player experience and ensure minimal latency, take the following steps when setting up your game session placement system:
+ Set your queue to prioritize latency when choosing where to place game sessions. Latency is at the top of the priority list by default. You can also customize your queue's priority configuration and choose where to put latency in priority order.
+ Set up player latency policies for your queue. Latency policies let you set hard limits on the amount of latency to allow in a game session placement. If Amazon GameLift Servers can't place a game session without exceeding the limits, the placement request will time out and fail. You can set up a single latency policy, or you can create a series of policies that gradually relax the latency limit over time. With a series of policies, you can specify very low initial latency limits, and still accommodate players with higher latencies after a short delay. For details on creating latency policies, see [Create a player latency policy](queues-design-latency.md).
+ When making game session placement requests (see [StartGameSessionPlacement](https://docs.aws.amazon.com/gameliftservers/latest/apireference/API_StartGameSessionPlacement.html)), include latency data for each player. Player latency data includes a value for every possible location where a game session might be placed. For example, for a queue that places game sessions in AWS Regions us-east-2 and ca-central-1, latency data might look like this:
```
"PlayerLatencies": [
{ "LatencyInMilliseconds": 100, "PlayerId": "player1", "RegionIdentifier": "us-east-2" },
{ "LatencyInMilliseconds": 100, "PlayerId": "player1", "RegionIdentifier": "ca-central-1" },
{ "LatencyInMilliseconds": 150, "PlayerId": "player2", "RegionIdentifier": "us-east-2" },
{ "LatencyInMilliseconds": 150, "PlayerId": "player2", "RegionIdentifier": "ca-central-1" }
]
```
To obtain accurate latency measurements, use Amazon GameLift Servers's UDP ping beacons. These endpoints enable you to measure actual UDP network latency between player devices and each of the potential hosting locations, resulting in more accurate placement decisions than using ICMP pings. For more information on using UDP ping beacons to measure latency, refer to [UDP ping beacons](reference-udp-ping-beacons.md).
## Prioritize placements by location
You can configure a queue to make game session placements based on a prioritized list of geographic locations. Location is one of the criteria that determines how a queue chooses where to place a new game session. By default, location is prioritized fourth, after latency, cost, and destination.
For game session placement, destination and location have somewhat different meanings:
+ *Destination* refers to a specific fleet and includes all the fleet's hosting resources, wherever they're deployed. When prioritizing by destination, Amazon GameLift Servers might make a placement with any location in the fleet. Multi-location managed fleets and Anywhere fleets can have hosting resources that are deployed to one or more locations.
+ *Location* refers to a specific geographic position where a fleet's hosting resources are deployed. A fleet can have multiple locations, which might include AWS Regions, Local Zones, or custom locations (for an Anywhere fleet). A single-location managed fleet has one location and it is always an AWS Region. A multi-location managed fleet has a home Region and can have remote locations. An Anywhere fleet has one or more custom locations.
When prioritizing placements by location, Amazon GameLift Servers looks for any queue destinations that include the priority location and searches them for an available hosting resource. If there are multiple destinations with the priority location, Amazon GameLift Servers moves on to the next priority criteria (cost, latency, destination).
There are several ways that you can influence how a queue's locations are prioritized
+ Configure how the queue handles all game session placement requests:
+ **Add a priority configuration to the queue.** A queue's priority configuration includes an ordered list of locations. You can specify one or more locations to prioritize. This list doesn't exclude any locations, it simply tells Amazon GameLift Servers where to look first for an available hosting resource. A common use for an ordered location list is when you want to funnel most traffic to one or more specific geographic locations and use additional locations as backup capacity. Add a priority configuration by calling [UpdateGameSessionQueue](https://docs.aws.amazon.com/gameliftservers/latest/apireference/API_UpdateGameSessionQueue.html).
+ **Add a filter configuration to the queue.** A filter configuration is an allow list for the queue. It tells Amazon GameLift Servers to ignore any locations that aren't on the list when looking for an available hosting resource. There are two common uses for a filter configuration. First, for fleets with multiple locations, you might use a filter to exclude some of the fleet's locations. Second, you might want to temporarily disallow placements on a certain location; for example, a location might be experiencing transitory issues. Because you can update a queue's filter configuration at any time, you can easily add and remove locations as needed. Add a filter configuration by calling [UpdateGameSessionQueue](https://docs.aws.amazon.com/gameliftservers/latest/apireference/API_UpdateGameSessionQueue.html).
+ Use special instructions for individual placement requests:
+ **Include a priority override list in a game session placement request.** You can provide an alternate priority list of locations with any [StartGameSessionPlacement](https://docs.aws.amazon.com/gameliftservers/latest/apireference/API_StartGameSessionPlacement.html) request. This list effectively replaces the queue's configured prioritization for locations for that one request only. It doesn't impact any other requests. This override feature has a few requirements:
+ Use an override list only with a queue that has a priority configuration in place with `LOCATION` as the first priority.
+ Don't include player latency data in the same placement request. Including latency data sets up conflicts when prioritizing locations that Amazon GameLift Servers can't resolve.
+ Decide how you want Amazon GameLift Servers to proceed if it can't find an available resource on the priority override list. Choose between falling back to the queue's other locations, or limit placements to the override list. By default, Amazon GameLift Servers falls back to attempt placement on the queue's other locations.
+ Update the queue's filter configuration as needed, such as adding locations on the override list. The override list doesn't invalidate the filter list.
# Create a player latency policy
If your placement requests include player latency data, Amazon GameLift Servers finds game sessions in locations with the lowest average latency for all players. Placing game sessions based on average player latency prevents Amazon GameLift Servers from placing most players in games with high latency. However, Amazon GameLift Servers still places players with extreme latency. To accommodate these players, create player latency policies.
A player latency policy prevents Amazon GameLift Servers from placing a requested game session anywhere that players in the request would experience latency over the maximum value. Player latency policies can also prevent Amazon GameLift Servers from matching game session requests with higher latency players.
**Tip**
To manage latency specific rules, such as requiring similar latency across all players in a group, you can use [Amazon GameLift Servers FlexMatch](https://docs.aws.amazon.com/gameliftservers/latest/flexmatchguide/match-intro.html) to create latency-based matchmaking rules.
For example, consider this queue with a 5-minute timeout and the following player latency policies:
1. Spend 120 seconds searching for a location where all player latencies are less than 50 milliseconds.
1. Spend 120 seconds searching for a location where all player latencies are less than 100 milliseconds.
1. Spend the remaining queue time until timeout searching for a location where all player latencies are less than 200 milliseconds.
![\[A console screen shot that illustrates the example latency policies that gradually relax.\]](http://docs.aws.amazon.com/gameliftservers/latest/developerguide/images/queue-latency-policy.png)