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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. This seamless behavior is a result of the next function triggers being routed to the swapped slot.
- Currently executing function are terminated during the swap. Please review Improve the performance and reliability of Azure Functions to learn how to write stateless and defensive functions.
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.
- Minimize restarts: Changing app settings in a production slot requires a restart of the running app. You can instead change settings in a staging slot and swap the settings change into production with a prewarmed instance. This is the recommended way to upgrade between Functions runtime versions while maintaining the highest availability. To learn more, see Minimum downtime upgrade.
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:
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)
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.
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.
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 settings before 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
- IP restrictions
- Always On
- Diagnostic settings
- Cross-origin resource sharing (CORS)
- Private endpoints
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
- 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:
Navigate to Deployment slots in the function app, and then select the slot name.
Select Configuration, and then select the setting name you want to stick with the current slot.
Select Deployment slot setting, and then select OK.
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:
Navigate to your function app.
Select Deployment slots, and then select + Add Slot.
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:
Navigate to the function app.
Select Deployment slots, and then select Swap.
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:
Navigate to Deployment slots in the function app, and then select the slot name.
Select Delete.
Type the name of the deployment slot you want to delete, and then select Delete.
Close the delete confirmation pane.
Automate slot management
Using the Azure CLI, you can automate the following actions for a slot:
- create
- delete
- list
- swap
- auto-swap
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:
Navigate to Deployment slots in the function app, and then select the slot name.
Under App Service plan, select Change App Service plan.
Select the plan you want to upgrade to, or create a new plan.
Select OK.
Considerations
Azure Functions deployment slots have the following considerations:
- 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 other plans. For details, see Service limits.
- Swapping a slot resets keys for apps that have an
AzureWebJobsSecretStorageTypeapp setting equal tofiles. - When slots are enabled, your function app is set to read-only mode in the portal.
- Use function app names shorter than 32 characters. Names longer than 32 characters are at risk of causing host ID collisons.
Next steps
- Deployment technologies in Azure Functions
FAQs
How many deployment slots does Azure have? ›
The Consumption plan is only allowed one deployment slot. Additional slots are available for apps running under other plans.
What is deployment slot setting in Azure function? ›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.
How many deployment slots we can get with standard tier of the app service plan? ›To scale your app to a different tier, make sure that the target tier supports the number of slots your app already uses. For example, if your app has more than five slots, you can't scale it down to the Standard tier, because the Standard tier supports only five deployment slots.
How can I improve my Azure function performance? ›- Avoid long running functions. ...
- Make sure background tasks complete. ...
- Cross function communication. ...
- Write functions to be stateless. ...
- Write defensive functions. ...
- Function organization best practices.
You can test the new version of your app using the testing in production feature. Deployment slots are great to verify a new version of an app before it goes live. Deployment slots are free!
How do you deploy 100 VMs in Azure? ›- Create up to 100 identical VMs using Azure DevTest Labs. ...
- Automatically create multiple VMs with the same base OS and configuration with Azure Virtual Machine Scale Sets. ...
- Rapidly create VMs using Azure CLI, PowerShell, ARM templates, and managed images.
From the menu select 'Deployment slots'. Now click on '+ Add Slot'. Set the 'Name' to staging and click on 'Add'. After the slot is created, we can publish the same app to the slot.
What are the 3 deployment modes that can be used for Azure? ›Azure supports three approaches to deploying cloud resources - public, private, and the hybrid cloud. Selecting between them will change several factors of the services you move into Azure including cost, maintenance requirements, and security.
What is the maximum number of deployment slots? ›Deployment slots are only supported in the Standard, Premium, and Isolated tiers. The Standard tier supports up to 5 slots, but the Premium and Isolated tiers support up to 20.
How many applications can you deploy to a single app service plan? ›You can host up to 100 apps in a single app service plan, but the key thing to know here is that as with the free plan you are charged per app, not per app service plan. Each instance of a web app you deploy in the shared plan get's it's own 240 CPU minutes limit and is charged per app.
How many resource groups can I deploy to in a single deployment operation? ›
Deploy to multiple resource groups
The resource groups can exist in different subscriptions. You can deploy to 800 resource groups in a single deployment.
Vendor-lock is the biggest drawback of this function. It is very difficult to run code deployed in Azure function outside the azure environment. The language used in function app such as java, NodeJS, etc are not specialized but the code to establish a connection between resources is specific to azure.
Can Azure functions be long running? ›With Durable Functions you can easily support long-running processes, applying the Async HTTP APIs or Monitoring Patterns. In case you are dealing with functions that require some time to process the payload or request consider running under an App Service Plan, WebJob, or Durable Functions.
What is the maximum run time for Azure functions? ›Regardless of the function app timeout setting, 230 seconds is the maximum amount of time that an HTTP triggered function can take to respond to a request.
How many additional deployment slots can you create in Azure? ›Deployment slots are a feature of Azure App Service Plans. As a result, every App Service resource (Web App, Web API, Mobile App) in Microsoft Azure has the ability to create up to 4 additional deployment slots with the Standard tiers, and up to 20 deployment slots with the Premium tiers.
Why build once deploy anywhere? ›Build once, deploy many is an essential principle of software development. The main idea is to use the same bundle for all environments, from testing to production. This approach enables easy deployment and testability and is considered a fundamental principle of continuous delivery.
Which deployment mode is suitable for most deployments? ›Digital Vaccine contain deployment settings for filters that address specific types of deployments. Provides a balance between high quality security and appliance performance, and is suitable for most deployments.
How many VMs can you have on Azure? ›You can create as many VMs as you want in Azure. However, it is recommended to create only what you need. You will be charged for the every VM in Azure.
How many number of Virtual machines can we scale upto on Azure *? ›How many VMs can I have in a scale set? A scale set can have 0 to 1,000 virtual machines (VMs) based on platform images, or 0 to 600 VMs based on custom images.
How do I increase VM quota in Azure? ›On the Overview page, select Compute. On the My quotas page, select the quota or quotas you want to increase. Near the top of the page, select Request quota increase, then select the way you'd like to increase the quota(s).
What is deployment slot setting? ›
Deployment Slot Setting
With this setting in place, database connection strings are not swapped when the slots are swapped. So staging slot will always point to the staging database and production slot will always point to the production database.
The magic of deployment slots: we can do swapping with zero downtime which means, end users will notice nothing and experience no downtime. Yes, users will experience no downtime. Therefore, this is one of the awesome features of Azure app services. Default app instance is always mapped to the production slot.
How do I enable continuous deployment? ›- Step 1: Create a deployment environment. ...
- Step 2: Get a copy of the sample code. ...
- Step 3: Create your pipeline. ...
- Step 4: Activate your pipeline to deploy your code. ...
- Step 5: Commit a change and then update your app. ...
- Step 6: Clean up your resources.
There are four cloud deployment models: public, private, community, and hybrid.
How many deployment models are used in Azure? ›There are three different ways to deploy cloud services: on a public cloud, private cloud or hybrid cloud.
What are the four cloud deployment types? ›4 Cloud Deployment Models with Examples: Public, Private, Community, Hybrid. There are many different models to choose from in regard to cloud deployments. Your cloud infrastructure and placement of each workload depends on your business needs.
How do I deploy Azure function to production? ›- Sign in to the Azure portal, and then go to your function app.
- On the Overview tab, select Download app content. Select your download options, and then select Download. The downloaded . zip file is in the correct format to be republished to your function app by using . zip push deployment.
Navigate to your Azure app service created in your environment. Click on the deployment slot in the left side panel and choose 'add slots' to create your staging environment. Give it a name like “Staging” so that it will be easy to identify.
How do I deploy multiple servers? ›Setting up a server group
Add a name for your server group, then select the default branch to deploy from. All servers within the group will then be deployed from the same branch. Next, you'll be able to choose how your servers are deployed, in parallel or sequentially.
Soldiers on active duty can be deployed anytime, for a period of 12 consecutive months or more sometimes. Soldiers in World War Two deployed for the entire war and could be gone for four to five years.
What is the average length of deployment? ›
The average military deployment is typically between six and 12 months long. However, deployment lengths vary greatly from branch to branch, are situational and depend on several factors specific to each individual service member.
What is the maximum number of unavailable pods? ›Default value for maxUnavailable is 25%
maxUnavailable is an optional field that specifies the maximum number of Pods that can be unavailable during the update process. The value can be an absolute number (for example, 5) or a percentage of desired Pods (for example, 10%).
To run multiple applications on the same server
Add an app to the stack for each application. Obtain a separate subdomain for each app and map the subdomains to the application server's or load balancer's IP address. Edit each app's configuration to specify the appropriate subdomain.
There's a maximum limit of 25 parallel jobs for Microsoft-hosted agents. Starting with Azure DevOps Server 2019, you do not have to pay for self-hosted concurrent jobs in releases.
Can same application be deployed to multiple spaces? ›No, there is no single command you can use to deploy the same application to different Orgs. The only workaround you can use is - create shell script to target different Org once you are done with push to one Org.
How many deployment slots we can get with standard tier of the APP service plan? ›To scale your app to a different tier, make sure that the target tier supports the number of slots your app already uses. For example, if your app has more than five slots, you can't scale it down to the Standard tier, because the Standard tier supports only five deployment slots.
What is the longest a deployment can be? ›What is the longest time of deployment? Deployment lengths in the Army can vary between 90 days and 15 months, however, many deployments are typically between six and 12 months. The length of an individual's deployment is contingent upon several factors, including: Deployment location.
How many slots are available in Azure cloud service? ›The Standard tier supports up to 5 slots, but the Premium and Isolated tiers support up to 20. So if you're using the Standard tier, and for some reason, you need more than 5 slots, you can just scale up your service plan to the Premium tier. And that's it for deployment slots in Azure App Service.
What are the deployment types in Azure? ›- External package URL. You can use an external package URL to reference a remote package (. ...
- Docker container. ...
- Web Deploy (MSDeploy) ...
- Source control. ...
- Local Git. ...
- Cloud sync. ...
- FTP. ...
- Portal editing.
Azure has several deployment models to consider when configuring a cloud solution. Specifically, there are three deployment models, and consist of what is called Public Cloud, Private Cloud, and Hybrid Cloud. Each deployment model has advantages and disadvantages based on the goals of the business use case.
How many additional deployment slots can you create in addition to the product deployment slot? ›
Expert-Verified Answer. In addition to the production deployment slot ,additional slots that can be created by us are out of the 5 deployment slots . The deployment slots which can be created can be swapped with various production slot or for another non productive slots.
How many additional deployment slots can you create in addition to the production develop deployment slot? ›In addition to the Production deployment slot, how many additional deployment slots can you create? You can add additional deployment slots for a total of 5 deployment slots that can be swapped with the production slot, or other non-production slots. The 4 additional slots can be used for staging and testing purposes.
How many requests can an Azure function handle? ›A single function app only scales out to a maximum of 200 instances. A single instance may process more than one message or request at a time though, so there isn't a set limit on number of concurrent executions.
How many hosting plans do Azure functions have? ›There are three basic hosting plans available for Azure Functions: Consumption plan, Premium plan, and Dedicated (App Service) plan.
What are the 3 deployment models? ›Each deployment model is defined according to where the infrastructure for the environment is located. There are three main cloud service models: Software as a Service, Platform as a Service, and Infrastructure as a Service.
What are the three types of cloud deployment? ›- Infrastructure as a Service (IaaS) ...
- Platform as a Service (PaaS) ...
- Software as a Service (SaaS)
Azure deployment slots are very useful. They allow you to run multiple versions of your application code on the same infrastructure. Let's understand the use of deployment slots with an example. Let's say you have a web application (MyWebApp) deployed in azure.
What is the most common deployment model? ›Which cloud deployment model is most commonly used? The public cloud is the most widely used model. It allows users to access a vast range of cloud-based services.