Cisco DNA Center HA Guide, Release 1.3.3.0
Refer to the following guide for a description of Cisco DNA Center's high availability (HA) implementation.
High Availability Overview
Cisco DNA Center’s HA framework is designed to reduce the amount of downtime that results from failures and make your network more resilient when they take place. When a failure occurs, this framework helps to restore your network to its previous operational state. If this is not possible, Cisco DNA Center will indicate that there is an issue requiring your attention.
Any time Cisco DNA Center’s HA framework determines that a change on a cluster node has taken place, it synchronizes this change with the other nodes. The supported synchronization types include:
-
Database changes, such as updates related to configuration, performance and monitoring data.
-
File changes, such as report configurations, configuration templates, TFTP-root directory, administration settings, licensing files, and the key store.
This guide covers the requirements that need to be met to use HA, deployment and administration best practices, and the failure scenarios you may encounter (as well as how Cisco DNA Center deals with them and any required user action).
In this release, Cisco DNA Center only provides HA support for Automation functionality. HA for Assurance is not supported at this time.
High Availability Requirements
To enable HA in your production environment, the following requirements must be met:
-
Your cluster consists of three Cisco DNA Center appliances with the same number of cores. This means that your cluster can consist of both the first generation 44 core appliance (Cisco part number DN1-HW-APL) and the second generation 44 core appliance (Cisco part numbers DN2-HW-APL and DN2-HW-APL-U).
Note
To view a listing of first and second generation appliances and their corresponding Cisco part number, see the "Interface Names and Wizard Configuration Order" topic in the Cisco Digital Network Architecture Center Second Generation Appliance Installation Guide.
-
The appliances are running the same version of Cisco DNA Center 1.2.8 or later. For example, if a patch for version 1.2.8 is installed on one cluster node, you must also install the same patch onto the other cluster nodes in order for HA to operate.
-
Multinode cluster deployments require all of the member nodes to be in the same network and at the same site. The Cisco DNA Center appliance does not support the distribution of nodes across multiple networks or sites.
High Availability Functionality
Cisco DNA Center supports a three-node cluster configuration, which provides both software and hardware high availability. A software failure occurs when a service on a node fails. Software high availability involves the ability of the services on the node or nodes to be restarted. For example, if a service fails on one node in a three-node cluster, that service is either restarted on the same node or on one of the other two remaining nodes. A hardware failure occurs when the appliance itself malfunctions or fails. Hardware high availability is enabled by the presence of multiple appliances in a cluster, multiple disk drives within each appliance's RAID configuration, and multiple power supplies. As a result, a failure by one of these components can be tolerated until the faulty component is restored or replaced.
![]() Note |
Cisco DNA Center does not support a cluster with more than three nodes. For example, a multi-node cluster with five or seven nodes is not currently supported. Fault tolerance for a three-node cluster is designed to handle single-node failure. In other words, Cisco DNA Center tries to provide high availability across specific services even if a single node fails. If two nodes fail, the quorum necessary to perform HA operations is lost and the cluster breaks. |
Clustering and Database Replication
Cisco DNA Center provides a mechanism for distributed processing and database replication among multiple nodes. Clustering provides both sharing of resources and features, as well as enabling high availability.
Security Replication
In a multi-node environment, the security features of a single node are replicated to the other two nodes, including any X.509 certificates or trustpools. After you join nodes to an existing cluster to form a three-node cluster, the Cisco DNA Center GUI user credentials are shared across the nodes. However, the CLI user credentials are not shared, because they are separate for each node.
Software Upgrade
In a multi-node cluster, you can trigger an upgrade of the whole cluster from the Cisco DNA Center GUI (the GUI represents the entire cluster and not just a single node). An upgrade triggered from the GUI automatically upgrades all the nodes in the cluster.
High Availability Deployment
The topics in this section cover the best practices you should follow when deploying and administering an HA-enabled cluster in your production environment.
Deployment Recommendations
We recommend that you set up a cluster consisting of three nodes: one seed node and two non-seed nodes. The odd number of nodes provides the quorum necessary to perform any operation in a distributed system such as this. Instead of three separate nodes, Cisco DNA Center views them as one logical entity accessed via a virtual IP address.
When deploying HA, we recommend the following:
-
When setting up a three-node cluster, do not configure the nodes to span a LAN across slow links, as this can make the cluster susceptible to network failures. It can also increase the amount of time needed for a service that fails on one of the nodes to recover. When configuring a three-node cluster's cluster interface, also ensure that all of the cluster nodes reside in the same subnet.
-
Avoid overloading a single interface with management, data, and HA responsibilities, as this might negatively impact HA operation.
-
When you are configuring cluster nodes, do not specify a link-local subnet (169.x.x.x) as the cluster or services subnet because its addresses are used by the Cisco DNA Center internal network.
Note
Subnets must conform with the IETF RFC 1918 and 6598 specifications for private networks, which support the following address ranges:
-
10.0.0.0/8
-
172.16.0.0/12
-
192.168.0.0/16
-
100.64.0.0/10
For details, see RFC 1918, Address Allocation for Private Internets, and RFC 6598, IANA-Reserved IPv4 Prefix for Shared Address Space.
-
-
Enable HA during off-hours, because Cisco DNA Center enters maintenance mode and is unavailable until it finishes redistributing services.
Deploy a Cluster
To deploy Cisco DNA Center on a three-node cluster with HA enabled, complete the following procedure:
Procedure
Step 1 |
Configure Cisco DNA Center on the first node in your cluster:
|
||
Step 2 |
Configure Cisco DNA Center on the second node in your cluster:
|
||
Step 3 |
Configure Cisco DNA Center on the third node in your cluster. Refer to the same add-on node configuration topic you viewed while completing Step 2. |
||
Step 4 |
Enable high availability on your cluster:
|
Administer a Cluster
The topics in this section cover the administrative tasks you will need to complete when HA is enabled in your production environment.
Run Maglev Commands
In order to run maglev commands successfully on the nodes in your cluster, do the following:
Before you begin
-
You only need to complete this procedure before you run the first maglev command in a session. You do not need to complete it again unless you close the current session and start a new one.
-
When you run a command in an SSH client, you may get an error message that indicates the RSA host key has been changed and prompts you to add the correct key to the ~/.ssh/known_hosts file. This typically happens when an appliance has been reimaged using a different IP address from the one that was specified for the appliance previously. If this happens, do the following:
-
Determine the IP address that is assigned to your appliance: cat ~/.ssh/known_hosts
where ~ represents the directory in which the known_host file resides on your machine.
The resulting output will look similar to the following example:
[192.168.254.21]:2222 ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBA19/31YV+cQvI1rmIVl/ CaE/BqCdeg5Xr/pSOtwNnKB6eDrXvLSAUMz+EED339GvbkxT/DdsdGZn2BeWHIifuY=
-
Remove all of the keys associated with this IP address from the known_hosts file: ssh-keygen -R appliance's-IP-address
Continuing our example, you would run the following command: ssh-keygen -R 192.168.254.21:2222
Note
Another option is to delete the ~/.ssh/known_hosts file before proceeding to the next step.
-
Run the command you tried to run previously.
-
Procedure
Step 1 |
In an SSH client, enter the following command: ssh node's-IP-address -l maglev -p 2222 |
Step 2 |
If you see a message indicating that the node's authenticity cannot be established, enter yes when prompted to continue. |
Step 3 |
Enter the Linux password configured for the node's maglev user. |
Step 4 |
Enter the maglev command that you want to run. |
Step 5 |
Enter the password configured for Cisco DNA Center's default admin superuser. |
Typical Cluster Node Operations
The following operations are the ones you will typically need to complete for the nodes in your cluster, such as shutting down a cluster node (which you would do before performing planned maintenance or preparing a node for Return Merchandise Authorization (RMA) and rebooting a node (which you would do to restore a node that has been down or save configuration changes).
![]() Note |
You cannot simultaneously reboot or shut down two nodes in an operational three-node cluster, as this breaks the cluster's quorum requirement. |
Operation | Required Actions | ||
---|---|---|---|
Shut down all of the nodes in a three node cluster from the CLI. |
Run the sudo shutdown -h now command on all of the nodes at the same time. |
||
Reboot one or more nodes after making any change that may require a reboot. |
Run the sudo shutdown -r now command on the relevant nodes. |
||
Shut down or disconnect one node for maintenance (in situations where you are not just rebooting the node). |
Run the following commands:
After performing maintenance on the node, complete the following steps:
|
||
Prepare a node for RMA. |
Do the following:
|
Replace a Failed Seed Node
If a seed node fails, complete the following tasks in order to replace it:
-
Remove the failed node from your cluster.
-
Replace the failed node with another node.
See Add a New Seed Node.
Remove the Failed Node
If a node fails because of a hardware failure, you'll need to remove it from the cluster. For assistance with this task, contact the Cisco TAC.
![]() Warning |
A two-node cluster (a transient configuration that's not supported for normal use) results when one of the following situations occur:
While a two-node cluster is active, you will not be able to remove either of its nodes. |
Add a New Seed Node
After removing the failed node, you can add the new node to the cluster.
Before you begin
Make sure that you complete the following tasks:
-
Remove the failed seed node. For information, see Remove the Failed Node.
-
Allocate at least 30 minutes to perform this procedure.
Procedure
Step 1 |
On the new node, install the same software version that the other nodes in the cluster are running.
|
||
Step 2 |
After the installation is complete, enter the following command: magctl node display The new node should show the Ready status. |
||
Step 3 |
From the new node, do the following: |
||
Step 4 |
If you previously backed up Assurance data, restore it. For information, see the "Restore Data from Backups" topic in the Cisco Digital Network Architecture Center Administrator Guide.
|
Minimize Failure and Outage Impact
In a typical three-node Cisco DNA Center cluster, each node is connected to a single cluster switch via the node’s cluster port interface. Connectivity with the cluster switch requires two transceivers and a fiber optic cable, any of which can fail. The cluster switch itself can also fail (due to things like a loss of power or manual restart), which can result in an outage of your Cisco DNA Center cluster and loss of all controller functionality. To minimize the impact of a failure or outage on your cluster, do one or more of the following:
-
Perform management operations such as software upgrades, configuration reloads, and power cycling during non-critical time periods, as these operations can result in a cluster outage.
-
Connect your cluster nodes to a switch that supports the in-service software upgrade (ISSU) feature. This feature allows you to upgrade system software while the system continues to forward traffic, using nonstop forwarding (NSF) with stateful switchover (SSO) to perform software upgrades with no system downtime.
-
Connect your cluster nodes to a switch stack, which allows you to connect each cluster node to a different member of the switch stack joined via Cisco StackWise. As the cluster is connected to multiple switches, the impact of one switch going down is mitigated.
High Availability Failure Scenarios
Nodes can fail due to issues in one or more of the following areas:
-
Software
-
Network access
-
Hardware
When a failure occurs, Cisco DNA Center normally detects it within 5 minutes and resolves the failure on its own. Failures that persist for longer than 5 minutes might require user intervention.
The following table describes failure scenarios your cluster might encounter and how Cisco DNA Center responds to them. Pay attention to the table's first column, which indicates the scenarios that require action from you in order to restore the operation of your cluster.
![]() Important |
For a cluster to operate, Cisco DNA Center's HA implementation requires at least two cluster nodes to be up at any given time. |
For information about known HA bugs and workarounds, see "Open Bugs—HA" in the Release Notes for Cisco Digital Network Architecture Center.
Requires User Action |
Failure Scenario |
HA Behavior |
---|---|---|
Yes |
Any node in the cluster goes down. |
Perform an Automation backup immediately. See the "Backup and Restore" chapter in the Cisco Digital Network Architecture Center Administrator Guide. |
No |
A node fails, is unreachable, or experiences a service failure for less than 5 minutes. |
After the node is restored:
|
No |
A non-seed node fails, is unreachable, or experiences a service failure for longer than 5 minutes. |
After the node is restored, and before the node rejoins the cluster:
After the node rejoins the cluster:
|
No |
A seed node fails, is unreachable, or experiences a service failure for longer than 5 minutes. |
After the node is restored, and before the node rejoins the cluster:
After the node rejoins the cluster:
|
Yes |
Two nodes fail or are unreachable. |
The cluster is broken and the UI is not accessible until connectivity has been restored.
|
Yes |
A node fails and needs to be removed from a cluster. |
Contact the Cisco TAC for assistance. |
No |
All nodes lose connectivity with one another. |
The UI is not accessible until connectivity has been restored. Once connectivity has been restored, operations resume and the data shared by cluster members is synced. |
Yes |
A backup is scheduled and a seed node goes down due to a hardware failure. |
Contact the Cisco TAC for a replacement node, as well as assistance with joining the new node to the cluster and restoring services on the two remaining nodes. |
Yes |
A red banner in the UI indicates that a node is down: "Assurance services are currently down. Connectivity with host <IP-address> has been lost." |
The banner indicates that the seed node is down, and Assurance data has been lost. If the seed node comes back up, your Assurance functionality is restored. But if the failure is related to a hardware failure, do the following:
|
Yes |
A red banner in the UI indicates that a node is down, but eventually changes to yellow with this message: "This IP address is down." |
The system is still usable. Investigate why the node is down, and bring it back up. |
Yes |
A failure occurs while upgrading a cluster. |
Contact the Cisco TAC for assistance. |
No |
An appliance port fails. |
|
Yes |
Appliance hardware fails. |
Replace the hardware component (such as a fan, power supply, or disk drive) that failed. Because multiple instances of these components are found in an appliance, the failure of one component can be tolerated temporarily. As the RAID controller syncs a newly added disk drive with the other drives on the appliance, there might be a degradation in performance on the I/O system while this occurs. |