DNS in Microsoft Azure – Part 2

DNS in Microsoft Azure – Part 2

Welcome back fellow geek to part two of my series on DNS in Azure.  In the first post I covered some core concepts behind the DNS offerings in Azure.  One of the core concepts was the 168.63.129.16 virtual IP address which acts the communication point when Azure services within a VNet need to talk to Azure DNS resolver.  If you’re unfamiliar with it, circle back and read that portion of the post.  I also covered the basic DNS offering, Azure-provided DNS.  For this post I’m going to cover the newly minted Azure Private DNS service.

As I covered my last post, Azure-provided DNS is a decent service if you’re doing some very basic proof-of-concept testing, but not much use beyond that.  The limited capabilities around record types, scale challenges for BYODNS when requiring resolution across multiple VNets, and no reverse DNS support typically have required an enterprise BYODNS solution.  This meant organizations were stuck purchasing expensive NVAs or rolling VMs running BIND or Windows DNS Server.  Beyond the overhead of having to manage all aspects of the VM we’re all familiar with, it also brings along legacy request and change management processes.  In most enterprises application owners have to submit requests to central IT to have DNS entries created or modified.  This is counter to the goal of empowering application owners to be more agile.

Thankfully, Microsoft heard the cries of application owners and central IT and introduced Azure Private DNS into public preview back in early 2018.  After a few iterations and improvements, the service officially went general availability just last month.  The service addresses many of the gaps Azure-provided DNS has such as:

  • Support for custom DNS namespaces
  • Support for all common DNS record types such as A, MX, CNAME, PTR
  • Support for reverse DNS
  • Automatic lifecycle management of VM DNS records
  • Resolution across multiple VNets

Before we jump into the weeds, we’ll first want to cover the basic concepts of the service.  Azure Private DNS zones are an Azure resource under the namespace of /providers/Microsoft.Network/privateDnsZones/.  Each DNS zone you want to create is represented as a separate resource.  Zones created in one subscription can be consumed in another subscription as long as they’re within the same Azure AD tenant.  VNets can resolve and register DNS records with the zones you create after you “link” the VNet to the zone.  Each zone can be linked to multiple VNets for registration and resolution.  On other hand, VNets can be linked to multiple zones for resolution but only one zone for registration.  Once a zone is linked to the VNet, VMs within the VNet resolve and/or register DNS records for those zones through the 168.63.129.16 virtual IP.

I’ll quickly cover the reverse lookup zone capability that comes along with using the service. When a VNet is linked to a zone for registration there is reverse lookup zone created for the VNet.  VMs created in subnets within that VNet will register a PTR record for its FQDN of the private zone as well as a PTR record for FQDN of internal.cloudapp.net zone.  Take note that records in the reverse lookup zone will only be resolvable by VMs within that VNet when sent through the 168.63.129.16 virtual IP.

In the image below VNet1 is linked to an Azure Private Zone for both resolution and registration.  VNet2 is registered to a different Azure Private Zone for both resolution and registration.  Both VNets are configured to use Azure DNS servers.  In this scenario, Server1 will be able to perform a reverse lookup for the IP address of Server2 because it is within the same VNet.  However, Server3 will not be able to perform a reverse lookup for Server2 because it is in a different VNet.

Picture of reverse DNS lookup flows

Reverse DNS Lookups with Azure Private DNS

In addition to PTR records, the VMs also register A records for the private zone and the Azure-provided DNS zone.  There are a few things to note about the A records automatically created in the private zone:

  • Each record has a property called isAutoRegistered which has a boolean value of true for any records created through the auto-registration process.
  • Auto-registered records have an extremely short TTL of 10 seconds.  If you have plans of performing DNS scavenging, take note of this and that these records are automatically deleted when the VM is deleted.
Private DNS zone viewed in portal

Portal View of Private DNS Zone

The Azure-provided DNS zone dynamically created for the VNet is still created even when linking an Azure Private DNS zone to a VNet.  Additionally, if you try to resolve the IP address using a single label hostname, you’ll get back the A record for the Azure-provided DNS zone.  This is by design and allows you to control the DNS suffix automatically appended by your VMs.  It also means you need to use the FQDN in any application configuration to ensure the record is resolved correctly.

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Let’s now look at resolution between two VNets.  In this scenario we again have VNet1 and VNet2.  VNet1 is linked for both registration and resolution to the Azure Private DNS Zone of app1zone.com.  VNet2 is linked for just resolution to the app1zone.com.  VMs in VNet2 are able to resolve queries for the fully-qualified domain name of VMs in VNet1 as illustrated in the diagram below.

Image showing DNS resolution between two VNets where both are linked for resolution

DNS Resolution between two VNets

Beyond the auto-registration of records, you can also manually create a variety of record types as I mentioned above. There isn’t anything special or different in the way Azure is handling these records.  The only thing worth noting is the records have a standard 1 hour TTL.

There are two significant limitations in the service right now.  One of those limitations is no support for query logging.  Given how important DNS query logging data can be as data points to identifying threats in the environment, your organization may require this.  If so, you’ll need to insert some BYODNS into the mix (I’ll cover that pattern next post).  The other bigger and more critical limitation is the lack of support for conditional forwarding.  As of today, you can’t create conditional forwarders for the service which will prevent you from forwarding queries from the 168.63.129.16 virtual IP to other DNS services you may have running for resolution of other resources such as on-premises resources.  Again, the workaround here is BYODNS.  Expect both of these limitations to be addressed in time as the service matures.

Azure Private DNS alone is a great service if your organization is completely in the cloud and has basic DNS resolution needs.  Some patterns you could leverage here:

  • Separate private DNS zone for each application –  In this scenario you could grant your application owners full control of the zone letting them manage the records as they see fit.  This would improve the application team’s agility while reducing operational burden on central IT.
  • Separate private DNS zones for each environment (Dev/QA/Prod) – In this scenario you could avoid having to do any BYODNS if there are no dependencies on on-premises infrastructure.  You also get full lifecycle management of VM records cutting back on operational overhead.

Summing up the service:

  • Positives
    • Managed service where you don’t have to worry the managing the underlining infrastructure
    • Scalability and availability are baked into the service
    • Use of custom DNS namespaces
    • VMs spread across multiple VNets can resolve each other’s addresses
    • Reverse DNS is supported within a VNet
    • Lifecycle of the VMs DNS records are automatically managed by the platform
    • Applications could be assigned their own DNS zones and application owners delegated full control over that zone
  • Negatives
    • No support for conditional forwarders at this time
    • No support for DNS query logging at this time
    • No support for WINS or NETBIOS (although I call this a positive 🙂 )

In my next post I’ll cover how the service works with BYODNS and will discuss some neat patterns that are available when you take advantage of the service.

A Comparison – AWS Managed Microsoft AD and Azure Active Directory Domain Services

A Comparison – AWS Managed Microsoft AD and Azure Active Directory Domain Services

Over the past year I’ve done deep dives into both Amazon’s AWS Managed Microsoft Active Directory and Microsoft’s Azure Active Directory Domain Services.  These services represent each vendor’s offering of a managed Windows Active Directory (AD) service.  I extensively covered the benefits of a service over the course of the posts, so today I’m going to cover the key features of each service.  I’m also going to include two tables.  One table will outline the differences in general features while the other outlines the differences in security-related features.

Let’s hit on the key points first.

  • Amazon provides a legacy (Windows AD is legacy folks) managed service while Microsoft provides a modernized service (Azure AD) which has been been integrated with a legacy service.
  • Microsoft synchronizes users, passwords hashes, and groups from the Azure AD to a managed instance of Windows Active Directory.  The reliance on this synchronization means the customer has to be comfortable synchronizing both directory data and password hashes to Azure AD.  Amazon does not require any data be synchronized.
  • Amazon provides the capability to leverage the identities in the managed instance of Windows AD or in a forest that has a trust with the managed instance to be leveraged in managing AWS resources.  In this instance Amazon is taking a legacy service and enabling it for management of the modern cloud management plane.
  • The pricing model for the services differs where Amazon bills on a per domain controller basis while Microsoft bills on the number of objects in the directory.
  • Amazon’s service is eligible to be used in solutions that require PCI DSS Level 1 or HIPAA.
  • Both services use a delegated model where the customer has full control over an OU rather the directory itself.  Highly privileged roles such as Schema Admin, Enterprise Admins, and Domain Admins are maintained by the cloud provider.
  • Both services provide LDAP for legacy applications customers may be trying to lift and shift.  Microsoft limits LDAP to read operations while Amazon supports both read and write operations.
  • Both services support LDAPS.  At this time Amazon requires an instance of Active Directory Certificate Services be deployed to act as a Certificate Authority and provide certificates to the managed domain controllers.
  • Both services do not allow the customer to modify the Default Domain Policy or Default Domain Controller Policies.  This means the customer cannot modify the password or lockout policy applied to the domain.  Amazon provides a method of enforcing custom password and lockout policies through Fine Grained Password Policies.  Additionally, the customer does not have the ability to harden the OS of the domain controllers for either service so it is important to review the vendor documentation.
  • Amazon’s service supports Active Directory forest trusts and external trusts.  Microsoft’s service doesn’t support trusts at this time.

Here is a table showing the comparison of general features:

Features AWS Managed Microsoft AD Azure Active Directory Domain Services
Cost Basis Number of Domain Controllers Number of Directory Objects
Schema Extensions Yes, with limitations No
Trusts Yes, with limitations No
Domain Controller Log Access Security and DNS Server Event Logs No
DNS Management Yes Yes
Snapshots Yes No
Limit of Managed Forests 10 per account 1 per Azure AD tenant
Supports being used on-premises Yes with Direct Connect or VPN No, within VNet only
Scaled By Customer Yes No
Max number of Domain Controller 20 per directory Unknown how service is scaled

Here is a table of security capabilities:

Features AWS Managed Microsoft AD Azure Active Directory Domain Services
Requires Directory Synchronization No Yes, including password
Fine-Grained Password Policies Yes, limited to seven No
Smart Card Authentication Not native, requires RADIUS No
LDAPS Yes, with special requirements Yes, but LDAP operations are limited to read
LDAPS Protocols SSLv3, TLS 1.0, TLS 1.2 TLS 1.0, TLS 1.2
LDAPS Cipher Suites RC4, 3DES, AES128, AES256 RC4, 3DES, AES128, AES256
Kerberos Delegation Account-Based and Resource-Based Resource-Based
Kerberos Encryption RC4, AES128, AES256 RC4, AES128, AES256
NTLM Support NTLMv1, NTLMv2 NTLMv1, NTLMv2

Well folks that sums it up.  As you can see from both of the series as well as this summary post both vendors have taken very different approaches in providing the service.  It will be interesting to see how these offerings evolve over the next few years.  As much as we’d love to see Windows Active Directory go away, it will still be here for years to come.

Until next time my fellow geeks!

AWS Managed Microsoft AD Deep Dive Part 7 – Trusts and Domain Controller Event Logs

AWS Managed Microsoft AD Deep Dive  Part 7 – Trusts and Domain Controller Event Logs

Welcome back fellow geek.  Today I’m continuing my deep dive series into AWS Managed Microsoft AD.  This will represent the seventh post in the series and I’ve covered some great content over the series including:

  1. An overview of the service
  2. How to setup the service
  3. The directory structure, pre-configured security principals, group policies and the delegated security model
  4. How to configure LDAPS and the requirements that pop up due to Amazon’s delegation model
  5. Security of the service including supported secure transport protocols, ciphers, and authentication protocols
  6. How do schema extensions work and what are the limitations

Today I’m going cover three additional capabilities of AWS Managed Microsoft AD which includes the creation of trusts, access to the Domain Controller event logs, and scalability.

I’ll first cover the capabilities around Active Directory trusts.  Providing this capability opens up the possibility a number of scenarios that aren’t possible in managed Windows Active Directory (Windows AD) services that don’t support trusts such as Microsoft’s Azure Active Directory Domain Services.  Some of the scenarios that pop up in my head are resource forest, trusts with trusted partners to maintain collaboration for legacy applications (applications dependent on legacy protocols such as Kerberos/NTLM/LDAP), trusts between development, QA, and production forests, and the usage of features features such as selective authentication to mitigate the risk to on-premises infrastructure.

For many organizations, modernization of an entire application catalog isn’t feasible but those organizations still want to take advantage of the cost and security benefits of cloud services.  This is where AWS Managed Microsoft AD can really shine.  It’s capability to support Active Directory forests trusts opens up the opportunity for those organizations to extend their identity boundary to the cloud while supporting legacy infrastructure.  Existing on-premises core infrastructure services such as PKI and SIEM can continue to be used and even extended to monitor the infrastructure using the managed Windows AD.

As you can see this is an extremely powerful capability and makes the service a good for almost every Windows AD scenario.  So that’s all well and good, but if you wanted marketing material you’d be reading the official documentation right?  You came here for the deep dive, so let’s get into it.

The first thing that popped into my mind was the question as to how Amazon would be providing this capability in a managed service model.  Creating a forest trust typically requires membership in privileged groups such as Enterprise Admins and Domain Admins, which obviously isn’t possible in a manged service.  I’m sure it’s possible to delegate the creation of Active Directory trusts and DNS conditional forwarders with modifications of directory permissions and possibly user rights, but there’s a better way.  What is this better way you may be asking yourself?  Perhaps serving it up via the Directory Services console in the same way schema modifications are served up?

Let’s walk through the process of setting up an Active Directory forest trust with a customer-managed traditional implementation of Windows Active Directory and an instance of AWS Managed Microsoft AD.  For this I’ll be leveraging my home Hyper-V lab.  I’m actually in the process of rebuilding it so there isn’t much there right now.  The home lab consists of two virtual machines, one named JOG-DC running Windows Server 2016 and functions as a domain controller (AD DS) and certificate authority (AD CS) for the journeyofthegeek.com Active Directory forest.  The other virtual machine is named named JOG-CLIENT, runs Windows 10, and is joined to the journeyofthegeek.com domain.  I’ve connected my VPC with my home lab using AWS’s Managed VPN to setup a site-to-site IPSec VPN connection with my local pfSense box.

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Prior to setting up the trusts there are a few preparatory steps that need to be completed.  The steps will be familiar to those of you who have established forests trusts across firewalled network segments.  At a high level, you’ll want to perform the following tasks:

  1. Ensure the appropriate ports are opened between the two forests.
  2. Ensure DNS resolution between the two forests is established

For the first step I played it lazy since this is is a temporary configuration (please don’t do this in production).   I allowed all traffic from the VPC address range to my lab environment by modifying the firewall rules on my pfSense box.  On the AWS side I needed to adjust the traffic rules for the security group SERVER01 is in as well as the security group for the managed domain controllers.

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To establish DNS resolution between the two forests I’ll be using conditional forwarders setup within each forest.  Setting the conditional forwarders up in the journeyofthegeek.com forest means I have to locate the IP addresses of the managed domain controllers in AWS.  There are a few ways you could do it, but I went to the AWS Directory Services Console and selected the geekintheweeds.com directory.

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On the Directory details section of the console the DNS addresses list the IP addresses the domain controllers are using.

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After creating the conditional forwarder in the DNS Management MMC in the journeyofthegeek.com forest, DNS resolution of a domain controller from geekintheweeds.com was successful.

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I next created the trust in the journeyofthegeek.com domain ensuring to select the option to create the trust in this domain only and recording the trust password using the Active Directory Domains and Trusts.  We can’t create the trusts in both domains since we don’t have an account with the appropriate privileges in the AWS managed domain.

Next up I bounced back over to the Directory Services console and selected the geekintheweeds.com directory.  From there I selected the Network & security tab to open the menu needed to create the trust.

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From here I clicked the Add trust relationship button which brings up the Add a trust relationship menu.  Here I filled in the name of the domain I want to establish the trust with, the trust password I setup in the journeyofthegeek.com domain, select a two-way trust, and add an IP that will be used within configuration of the conditional forwarder setup by the managed service.

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After clicking the Add button the status of the trust is updated to Creating.

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The process takes a few minutes after which the status reports as verified.

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Opening up the Active Directory Users and Computers (ADUC) MMC in the journeyofthegeek.com domain and selecting the geekintheweeds.com domain successfully displays the directory structure.  Trying the opposite in the geekintheweeds.com domain works correctly as well.  So our two-way trust has been created successfully.  We would now have the ability to setup any of the scenarios I talked about earlier in the post including a resource forest or leveraging the managed domain as a primary Windows AD service for on-premises infrastructure.

The second capability I want to briefly touch on is the ability to view the Security Event Log and DNS Server logs on the managed domain controllers.  Unlike Microsoft’s managed Windows AD service, Amazon provides ongoing access to the Security Event Log and DNS Server Log.  The logs can be viewed using the Event Log MMC from a domain-joined machine or programmatically with PowerShell.  The group policy assigned to the Domain Controllers OU enforces a maximum event log size of 256MB but Amazon also archives a year’s worth of logs which can be requested in the event of an incident.  The lack of this capability was a big sore spot for me when I looked at Azure Active Directory Domain Services.  It’s great to see Amazon has identified this critical use case.

Last but definitely not least, let’s quickly cover the scalability of the service.  Follow Microsoft best practices and you can take full advantage of scaling horizontally with the click of a single button.  Be aware that the service only scales horizontally and not vertically.  If you have applications that don’t follow best practices and point to specific domain controllers or perform extremely inefficient LDAP queries (yes I’m talking to you developers who perform searches using front and rear-facing wildcards and use LDAP_MATCHING_RULE_IN_CHAIN filters) horizontal scaling isn’t going to help you.

Well folks that rounds out this entry into the series.  As we saw in the post Amazon has added key capabilities that Microsoft’s managed service is missing right now.  This makes AWS Managed Microsoft AD the more versatile of the two services and more than likely a better fit in almost any scenario where there is a reliance on Windows AD.

In my final posts of the series I’ll provide a comparison chart showing the differing capabilities of both AWS and Microsoft’s services.

See you next post!

 

 

 

AWS Managed Microsoft AD Deep Dive Part 6 – Schema Modifications

AWS Managed Microsoft AD Deep Dive  Part 6 – Schema Modifications

Yes folks, we’re at the six post for the series on AWS Managed Microsoft AD (AWS Managed AD.  I’ve covered a lot of material over the series including an overview, how to setup the service, the directory structure, pre-configured security principals, group policies, and the delegated security model, how to configure LDAPS in the service and the implications of Amazon’s design, and just a few days ago looked at the configuration of the security of the service in regards to protocols and cipher suites.  As per usual, I’d highly suggest you take a read through the prior posts in the series before starting on this one.

Today I’m going to look the capabilities within the AWS Managed AD to handle Active Directory schema modifications.  If you’ve read my series on Microsoft’s Azure Active Directory Domain Services (AAD DS) you know that the service doesn’t support the schema modifications.  This makes Amazon’s service the better offering in an environment where schema modifications to the standard Windows AD schema are a requirement.  However, like many capabilities in a managed Windows Active Directory (Windows AD) service, limitations are introduced when compared to a customer-run Windows Active Directory infrastructure.

If you’ve administered an Active Directory environment in a complex enterprise (managing users, groups, and group policies doesn’t count) you’re familiar with the butterflies that accompany the mention of a schema change.  Modifying the schema of Active Directory is similar to modifying the DNA of a living being.  Sure, you might have wonderful intentions but you may just end up causing the zombie apocalypse.  Modifications typically mean lots of application testing of the schema changes in a lower environment and a well documented and disaster recovery plan (you really don’t want to try to recover from a failed schema change or have to back one out).

Given the above, you can see the logic of why a service provider providing a managed Windows AD service wouldn’t want to allow schema changes.  However, there very legitimate business justifications for expanding the schema (outside your standard AD/Exchange/Skype upgrades) such as applications that need to store additional data about a security principal or having a business process that would be better facilitated with some additional metadata attached to an employee’s AD user account.  This is the market share Amazon is looking to capture.

So how does Amazon provide for this capability in a managed Windows AD forest?  Amazon accomplishes it through a very intelligent method of performing such a critical activity.  It’s accomplished by submitting an LDIF through the AWS Directory Service console.  That’s right folks, you (and probably more so Amazon) doesn’t have to worry about you as the customer having to hold membership in a highly privileged group such as Schema Admins or absolutely butchering a schema change by modifying something you didn’t intend to modify.

Amazon describes three steps to modifying the schema:

  1. Create the LDIF file
  2. Import the LDIF file
  3. Verify the schema extension was successful

Let’s review each of the steps.

In the first step we have to create a LDAP Data Interchange Format (LDIF) file.  Think of the LDIF file as a set of instructions to the directory which in this could would be an add or modify to an object class or attribute.  I’ll be using a sample LDIF file I grabbed from an Oracle knowledge base article.  This schema file will add the attributes of unixUserName, unixGroupName, and unixNameIinfo to the default Active Directory schema.

To complete step one I dumped the contents below into an LDIF file and saved it as schemamod.ldif.

dn: CN=unixUserName, CN=Schema, CN=Configuration, DC=example, DC=com
changetype: add
attributeID: 1.3.6.1.4.1.42.2.27.5.1.60
attributeSyntax: 2.5.5.3
isSingleValued: TRUE
searchFlags: 1
lDAPDisplayName: unixUserName
adminDescription: This attribute contains the object's UNIX username
objectClass: attributeSchema
oMSyntax: 27

dn: CN=unixGroupName, CN=Schema, CN=Configuration, DC=example, DC=com
changetype: add
attributeID: 1.3.6.1.4.1.42.2.27.5.1.61
attributeSyntax: 2.5.5.3
isSingleValued: TRUE
searchFlags: 1
lDAPDisplayName: unixGroupName
adminDescription: This attribute contains the object's UNIX groupname
objectClass: attributeSchema
oMSyntax: 27

dn:
changetype: modify
add: schemaUpdateNow
schemaUpdateNow: 1
-

dn: CN=unixNameInfo, CN=Schema, CN=Configuration, DC=example, DC=com
changetype: add
governsID: 1.3.6.1.4.1.42.2.27.5.2.15
lDAPDisplayName: unixNameInfo
adminDescription: Auxiliary class to store UNIX name info in AD
mayContain: unixUserName
mayContain: unixGroupName
objectClass: classSchema
objectClassCategory: 3
subClassOf: top

For the step two I logged into the AWS Management Console and navigated to the Directory Service Console.  Here we can see my instance AWS Managed AD with the domain name of geekintheweeds.com.

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I then clicked hyperlink on my Directory ID which takes me into the console for the geekintheweeds.com instance.  Scrolling down shows a menu where a number of operations can be performed.  For the purposes of this blog post, we’re going to focus on the Maintenance menu item.  Here we the ability to leverage AWS Simple Notification Service (AWS SNS) to create notifications for directory changes such as health changes where a managed Domain Controller goes down.  The second section is a pretty neat feature where we can snapshot the Windows AD environment to create a point-in-time copy of the directory we can restore.  We’ll see this in action in a few minutes.  Lastly, we have the schema extensions section.

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Here I clicked the Upload and update schema button and entered selected the LDIF file and added a short description.  I then clicked the Update Schema button.

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If you know me you know I love to try to break stuff.  If you look closely at the LDIF contents I pasted above you’ll notice I didn’t update the file with my domain name.  Here the error in the LDIF has been detected and the schema modification was cancelled.

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I went through made the necessary modifications to the file and tried again.  The LDIF processes through and the console updates to show the schema change has been initialized.

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Hitting refresh on the browser window updates the status to show Creating Snapshot.  Yes folks Amazon has baked into the schema update process a snapshot of the directory provide a fallback mechanism in the event of your zombie apocalypse.  The snapshot creation process will take a while.

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While the snapshot process, let’s discuss what Amazon is doing behind the scenes to process the LDIF file.  We first saw that it performs some light validation on the LDIF file, it then takes a snapshot of the directory, then applies to the changes to a single domain controller by selecting one as the schema master, removing it from directory replication, and applying the LDIF file using the our favorite old school tool LDIFDE.EXE.  Lastly, the domain controller is added back into replication to replicate the changes to the other domain controller and complete the changes.  If you’ve been administering Windows AD you’ll know this has appeared recommended best practices for schema updates over the years.

Once the process is complete the console updates to show completion of the schema installation and the creation of the snapshot.

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