• ‘When placed into a slot that fits the screw's groove and shape, this allows for rotary motion to be converted into forward or backward motion.’ ‘It's easy to find a bit that fits the screw slot properly.’ ‘Of course, the screw slot is pretty fine, so without a properly fitting screwdriver, there is a real risk of marring things.’.
• In computers, a slot, or expansion slot, is an engineered technique for adding capability to a computer in the form of connection pinholes (typically, in the range of 16 to 64 closely-spaced holes) and a place to fit an expansion card containing the circuitry that provides some specialized capability, such as video acceleration, sound, or disk drive control.

The new slot is now shown on the Deployment slots page. By default, Traffic% is set to 0 for the new slot, with all customer traffic routed to the production slot. Select the new deployment slot to open that slot's resource page. The staging slot has a management page just like any other App Service app. You can change the slot's configuration.

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Azure Functions deployment slots allow your function app to run different instances called 'slots'. Slots are different environments exposed via a publicly available endpoint. One app instance is always mapped to the production slot, and you can swap instances assigned to a slot on demand. Function apps running under the Apps Service plan may have multiple slots, while under the Consumption plan only one slot is allowed.

The following reflect how functions are affected by swapping slots:

• Traffic redirection is seamless; no requests are dropped because of a swap.
• If a function is running during a swap, execution continues and the next triggers are routed to the swapped app instance.

Note

Slots are currently not available for the Linux Consumption plan.

Why use slots?

There are a number of advantages to using deployment slots. The following scenarios describe common uses for slots:

• Different environments for different purposes: Using different slots gives you the opportunity to differentiate app instances before swapping to production or a staging slot.
• Prewarming: Deploying to a slot instead of directly to production allows the app to warm up before going live. Additionally, using slots reduces latency for HTTP-triggered workloads. Instances are warmed up before deployment, which reduces the cold start for newly deployed functions.
• Easy fallbacks: After a swap with production, the slot with a previously staged app now has the previous production app. If the changes swapped into the production slot aren't as you expect, you can immediately reverse the swap to get your 'last known good instance' back.

Swap operations

During a swap, one slot is considered the source and the other the target. The source slot has the instance of the application that is applied to the target slot. The following steps ensure the target slot doesn't experience downtime during a swap:

1. Apply settings: Settings from the target slot are applied to all instances of the source slot. For example, the production settings are applied to the staging instance. The applied settings include the following categories:

   • Slot-specific app settings and connection strings (if applicable)
   • Continuous deployment settings (if enabled)
   • App Service authentication settings (if enabled)

2. Wait for restarts and availability: The swap waits for every instance in the source slot to complete its restart and to be available for requests. If any instance fails to restart, the swap operation reverts all changes to the source slot and stops the operation.

3. Update routing: If all instances on the source slot are warmed up successfully, the two slots complete the swap by switching routing rules. After this step, the target slot (for example, the production slot) has the app that's previously warmed up in the source slot.

4. Repeat operation: Now that the source slot has the pre-swap app previously in the target slot, complete the same operation by applying all settings and restarting the instances for the source slot.

Keep in mind the following points:

• At any point of the swap operation, initialization of the swapped apps happens on the source slot. The target slot remains online while the source slot is prepared, whether the swap succeeds or fails.

• To swap a staging slot with the production slot, make sure that the production slot is always the target slot. This way, the swap operation doesn't affect your production app.

• Settings related to event sources and bindings must be configured as deployment slot settingsbefore you start a swap. Marking them as 'sticky' ahead of time ensures events and outputs are directed to the proper instance.

Manage settings

Some configuration settings are slot-specific. The following lists detail which settings change when you swap slots, and which remain the same.

Slot-specific settings:

• Publishing endpoints
• Custom domain names
• Non-public certificates and TLS/SSL settings
• Scale settings
• WebJobs schedulers
• IP restrictions
• Always On
• Diagnostic settings
• Cross-origin resource sharing (CORS)

Non slot-specific settings:

• General settings, such as framework version, 32/64-bit, web sockets
• App settings (can be configured to stick to a slot)
• Connection strings (can be configured to stick to a slot)
• Handler mappings
• Public certificates
• WebJobs content
• Hybrid connections *
• Virtual network integration *
• Service endpoints *
• Azure Content Delivery Network *

Features marked with an asterisk (*) are planned to be unswapped.

Note

Certain app settings that apply to unswapped settings are also not swapped. For example, since diagnostic settings are not swapped, related app settings like WEBSITE_HTTPLOGGING_RETENTION_DAYS and DIAGNOSTICS_AZUREBLOBRETENTIONDAYS are also not swapped, even if they don't show up as slot settings.

Create a deployment setting

You can mark settings as a deployment setting, which makes it 'sticky'. A sticky setting doesn't swap with the app instance.

If you create a deployment setting in one slot, make sure to create the same setting with a unique value in any other slot that is involved in a swap. This way, while a setting's value doesn't change, the setting names remain consistent among slots. This name consistency ensures your code doesn't try to access a setting that is defined in one slot but not another.

Use the following steps to create a deployment setting:

1. Navigate to Deployment slots in the function app, and then select the slot name.

2. Select Configuration, and then select the setting name you want to stick with the current slot.

3. Select Deployment slot setting, and then select OK.

4. Once setting section disappears, select Save to keep the changes

Deployment

Slots are empty when you create a slot. You can use any of the supported deployment technologies to deploy your application to a slot.

Scaling

All slots scale to the same number of workers as the production slot.

• For Consumption plans, the slot scales as the function app scales.
• For App Service plans, the app scales to a fixed number of workers. Slots run on the same number of workers as the app plan.

Add a slot

You can add a slot via the CLI or through the portal. The following steps demonstrate how to create a new slot in the portal:

1. Navigate to your function app.

2. Select Deployment slots, and then select + Add Slot.

3. Type the name of the slot and select Add.

Swap slots

You can swap slots via the CLI or through the portal. The following steps demonstrate how to swap slots in the portal:

1. Navigate to the function app.

2. Select Deployment slots, and then select Swap.

3. Verify the configuration settings for your swap and select Swap

The operation may take a moment while the swap operation is executing.

Roll back a swap

If a swap results in an error or you simply want to 'undo' a swap, you can roll back to the initial state. To return to the pre-swapped state, do another swap to reverse the swap.

Remove a slot

You can remove a slot via the CLI or through the portal. The following steps demonstrate how to remove a slot in the portal:

1. Navigate to Deployment slots in the function app, and then select the slot name.

2. Select Delete.

3. Type the name of the deployment slot you want to delete, and then select Delete.

4. Close the delete confirmation pane.

Automate slot management

Using the Azure CLI, you can automate the following actions for a slot:

Change App Service plan

With a function app that is running under an App Service plan, you can change the underlying App Service plan for a slot.

Note

You can't change a slot's App Service plan under the Consumption plan.

Use the following steps to change a slot's App Service plan:

1. Navigate to Deployment slots in the function app, and then select the slot name.

2. Under App Service plan, select Change App Service plan.

3. Select the plan you want to upgrade to, or create a new plan.

4. Select OK.

Limitations

Azure Functions deployment slots have the following limitations:

• The number of slots available to an app depends on the plan. The Consumption plan is only allowed one deployment slot. Additional slots are available for apps running under the App Service plan.
• Swapping a slot resets keys for apps that have an AzureWebJobsSecretStorageType app setting equal to files.
• Slots aren't available for the Linux Consumption plan.

Support levels

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There are two levels of support for deployment slots:

• General availability (GA): Fully supported and approved for production use.
• Preview: Not yet supported, but is expected to reach GA status in the future.

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Next steps

Slot, the slot or Slots may refer to:

People[edit]

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• Arne Slot (born 1978), Dutch footballer
• Gerrie Slot (born 1954), Dutch cyclist
• Hanke Bruins Slot (born 1977), Dutch politician
• Tonny Bruins Slot (born 1947), Dutch association football coach who is known for his analyses of matches and opponents
• Jørgen Slots, a Danish-born periodontist in the United States
• Margareta Slots (died 1669), Dutch-born mistress of Gustav II Adolf of Sweden

Arts, entertainment, and media[edit]

Music[edit]

• Slot (band), a Russian alternative/nu metal band
• Slot, abbreviation of St. Laurence O'Toole Pipe Band, a pipe band based in Dublin, Ireland

Other uses in arts, entertainment, and media[edit]

• Dance slot, an imaginary narrow rectangle along which a follower moves back and forth with respect to the leader
• The Slot (TV series), an Australian television series

Sport[edit]

• Slot (ice hockey), the area on the hockey rink directly ahead of the goaltender between the faceoff circles on each side
• Slot, a space within a formation during a game of American football; see Glossary of American football

Technology[edit]

• Slot (computer architecture), the operation issue and data path machinery associated with a single execute pipeline in a CPU
• Expansion slot, portion of a computer mother board that can receive an expansion card
• Kensington Security Slot, a small hole found on almost all recent small or portable computer and electronics equipment used for attaching a lock
• Leading-edge slot, a fixed aerodynamic feature of the wing of some aircraft to reduce the stall speed
• Slot antenna, a directional antenna consisting of a slot in a piece of metal

Other uses[edit]

• Landing slot, a right allocated to an airline by an airport or government agency to schedule a landing or departure at a specific time
• Train slot, a license allocated to a rail transport company
• Mail slot or letter box, a receptacle for receiving incoming mail
• Orbital slot, an allotted position for a satellite in a 'crowded' orbit
• Slot machine, a type of casino game
• Slot man or The slot, slang term for the chief copy editor on a newspaper
• 'The Slot' or New Georgia Sound, a sound in the Solomon Islands known to Allied combatants during World War II
• The Slot, a gay hotel and sex club featured in the Folsom Street Fair in San Francisco

See also[edit]

• Groove (engineering), a feature cut into a hard material to provide a location for another component
• Tongue and groove, a type of joinery employing slots and interlocking ridges cut into material

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