Umbraco in Load Balanced Environments

    Information on how to deploy Umbraco in a Load Balanced scenario and other details to consider when setting up Umbraco for load balancing.


    Configuring and setting up a load balanced server environment requires planning, design and testing. This document should assist you in setting up your servers, load balanced environment and Umbraco configuration.

    This document assumes that you have a fair amount of knowledge about:

    • Umbraco
    • IIS 7+
    • Networking & DNS
    • Windows Server
    • .NET Framework v4.7.2+

    It is highly recommended that you setup your staging environment to also be load balanced so that you can run all of your testing on a similar environment to your live environment.


    These instructions make the following assumptions:

    • All web servers can communicate with the database where Umbraco data is stored
    • You are running Umbraco 8.1.0 or above
    • You will designate a single server to be the backoffice server for which your editors will log into for editing content. Umbraco will not work correctly if the backoffice is behind the load balancer.

    There are three design alternatives you can use to effectively load balance servers:

    1. You use cloud based auto-scaling appliances like Microsoft's Azure Web Apps
    2. Each server hosts copies of the load balanced website files and a file replication service is running to ensure that all files on all servers are up to date
    3. The load balanced website files are located on a centralized file share (SAN/NAS/Clustered File Server/Network Share)

    You will obviously need a load balancer to do your load balancing!

    How Umbraco load balancing works

    In order to understand how to host your site it is best to understand how Umbraco's flexible load balancing works.

    The following diagram shows the data flow/communication between each item in the environment:

    Umbraco flexible load balancing diagram

    The process is as follows:

    • Administrators and editors create, update, delete data/content on the master server
    • These events are converted into data structures called "instructions" and are stored in the database in a queue
    • Each front-end server checks to see if there are any outstanding instructions it hasn't processed yet
    • When a front-end server detects that there are pending instructions, it downloads them and processes them and in turn updates it's cache, cache files and indexes on its own file system
    • There can be a delay between content updates and a front-end server's refreshing, this is expected and normal behaviour.

    Scheduling and master election

    Although there is a Master server designated for administration, by default this is not explicitly set as the "Scheduling server". In Umbraco there can only be a single scheduling server which performs the following 3 things:

    • Keep alive service - to ensure scheduled publishing occurs
    • Scheduled tasks - to initiate any configured scheduled tasks
    • Scheduled publishing - to initiate any scheduled publishing for documents

    Umbraco will automatically elect a "Scheduling server" to perform the above services. This means that all of the servers will need to be able to resolve the URL of either: itself, the Master server, the internal load balancer or the public address.

    For example, In the following diagram the replica node f02.mysite.local is the elected "Scheduling server". In order for scheduling to work it needs to be able to send requests to itself, the Master server, the internal load balancer or the public address. The address used by the "Scheduling server" is called the "umbracoApplicationUrl".

    Umbraco flexible load balancing diagram

    By default, Umbraco will set the "umbracoApplicationUrl" to the address made by the first accepted request when the AppDomain starts. It is assumed that this address will be a DNS address that the server can resolve.

    For example, if a public request reached the load balancer on, the load balancer may send the request on to the servers with the original address: By default the "umbracoApplicationUrl" will be However, load balancers may route the request internally under a different DNS name such as "f02.mysite.local" which by default would mean the "umbracoApplicationUrl" is "f02.mysite.local". In any case the elected "Scheduling server" must be able to resolve this address.

    In many scenarios this is fine, but in case this is not adequate there's a few of options you can use:

    Common load balancing setup information

    _The below section applies to all ASP.NET load balancing configurations.

    Machine Key

    • You will need to use a custom machine key so that all your machine key level encryption values are the same on all servers, without this you will end up with view state errors, validation errors and encryption/decryption errors since each server will have its own generated key.
    • You need to update your web.config accordingly, note that the validation/decryption types may be different for your environment depending on how you've generated your keys.
    • Umbraco offers the opportunity to auto generate a machine key during the installation steps so this may already exist
        <machineKey decryptionKey="Your decryption key here"
                    validationKey="Your Validation key here"
                    decryption="AES" />

    Session State

    • If you use SessionState in your application, or are using the default TempDataProvider in MVC (which uses SessionState) then you will need to configure your application to use the SqlSessionStateStore or an alternative provider (see for more details).


    There are some logging configurations to take into account no matter what type of load balancing environment you are using.

    Full documentation is available here


    Your staging environment should also be load balanced so that you can see any issues relating to load balancing in that environment before going to production.

    You'll need to test this solution a lot before going to production. You need to ensure there are no windows security issues, etc... The best way to determine issues is have a lot of people testing this setup and ensuring all errors and warnings in your application/system logs in Windows are fixed.

    Ensure to analyze logs from all servers and check for any warnings and errors.

    File system replication

    There are various configuration options that need to be considered depending on your infrastructure set-up.

    Full documentation is available here


    Here's some common questions that are asked regarding Load Balancing with Umbraco:

    Question> Why do I need to have a single web instance for Umbraco admin?

    TL:DR You must not load balance the Umbraco backoffice, you will end up with data integrity or corruption issues.

    The reason you need a single server is because there is no way to guarantee transactional safety between servers. This is because we don't currently use database level locking, we only use application (c#) level locks to guarantee transactional data integrity which is only possible to work on one server. If you have multiple admins saving and publishing at once between servers then the order in which this data is read and written to the database absolutely must be consistent otherwise you will end up with data corruption.

    Additionally the order in which cache instructions are written to the cache instructions table is very important for LB, this order is guaranteed by having a single admin server.

    Question> Can my Master admin server also serve front-end requests?

    Yes. There are no problems with having your master admin server also serve front-end request.

    However, if you wish to have different security policies for your front-end servers and your back office servers, you may choose to not do this.