Cisco DNA Center High Availability Guide, Release 2.2.1
Refer to the following guide for a description of Cisco DNA Center's high availability (HA) implementation.
 Note |
For a description of disaster recovery functionality in Cisco DNA Center, see the "Implement Disaster Recovery" chapter in the Cisco DNA Center Administrator Guide. |
Note |
The documentation set for this product strives to use bias-free language. For purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. Exceptions may be present in the documentation due to language that is hardcoded in the user interfaces of the product software, language used based on RFP documentation, or language that is used by a referenced third-party product. |
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. It does so by providing the near real-time synchronization of changes across your cluster nodes, giving your network a level of redundancy to deal with any issues that arise. The supported synchronization types include:
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Database changes, such as updates related to configuration, performance and monitoring data.
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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).
Important |
Cisco DNA Center provides HA support for both Automation and Assurance functionality. |
High Availability Requirements
To enable HA in your production environment, the following requirements must be met:
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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 "Maglev Wizard Interface Configuration Order" topic in the Cisco DNA Center Second-Generation Appliance Installation Guide.
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Your secondary appliances are running the same version of Cisco DNA Center (1.2.8 or later) as the primary appliance.
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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.
Note |
After you initiate a system upgrade (which updates Cisco DNA Center's core infrastructure), Cisco DNA Center goes into maintenance mode. In maintenance mode, Cisco DNA Center will be unavailable until the upgrade process completes. You should take this into account when scheduling a system upgrade. Once the system upgrade does complete, you can verify its success in the GUI by accessing and checking the installed version.
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) and choose 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
Cisco DNA Center supports three-node clusters. 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:
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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.
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Avoid overloading a single interface with management, data, and HA responsibilities, as this might negatively impact HA operation.
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In the appliance configuration wizards, Cisco DNA Center prepopulates the Services Subnet and Cluster Services Subnet fields with link-local (169.x.x.x) subnets. We recommend that you use the default subnets, but you can choose to specify different subnets. If you do so, they must conform with the IETF RFC 1918 and 6598 specifications for private networks, which support the following address ranges:
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10.0.0.0/8
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172.16.0.0/12
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192.168.0.0/16
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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.
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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:
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| Step 2 |
Configure Cisco DNA Center on the second node in your cluster:
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| Step 3 |
Configure Cisco DNA Center on the third node in your cluster. Refer to the same secondary appliance configuration topic you viewed while completing Step 2. |
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| Step 4 |
Activate high availability on your cluster:
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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
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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.
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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:
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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.
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Run the command you tried to run previously.
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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), preparing a node for Return Merchandise Authorization (RMA), or rebooting (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 |
|---|---|
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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. |
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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. |
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Shut down or disconnect one node for maintenance (in situations where you are not just rebooting the node). |
Run the following commands:
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Prepare a node for RMA. |
Do the following:
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Recover a Failed Cluster Node
To recover a node in your cluster that has failed, do the following:
Procedure
| Step 1 |
Contact the Cisco TAC for assistance with removing the faulty node from your cluster. |
| Step 2 |
Enter the maglev package status command on the active node. You can also access this information from the Cisco DNA Center GUI by clicking the Help icon ( |
| Step 3 |
Contact the Cisco TAC, give them the output of that command, and ask for an ISO that matches your version. |
| Step 4 |
To add back the removed node, you must reinstall it.
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| Step 5 |
Activate high availability on your cluster:
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) and choosing Replace a Failed Node
If a node fails, complete the following tasks in order to replace it:
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Remove the failed node from your cluster.
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Replace the failed node with another node.
Remove the Failed Node
If a node fails, you must remove it so that you can replace it with a working node.
This section applies only if the failure is due to a hardware failure.
Before you begin
Make sure that you have a backup of your data. If you are performing this procedure due to a node failure, you cannot create a backup now. Instead, you must rely on backups that you have been routinely creating.
Procedure
| Step 1 |
Shut down the node that you want to remove. The shutdown process takes about 10 minutes. |
| Step 2 |
Verify that the node is down: magctl node display The node status should be NotReady. |
| Step 3 |
Check the appstack status: magctl appstack status The pods for the node that was shut down should show NODE LOST or Pending as their status. |
| Step 4 |
Log in to one of the nodes that you are not removing: maglev login -u admin -p admin-password -c node's-IP-address:443 |
| Step 5 |
Contact the Cisco TAC for assistance with removing the faulty node from your cluster. |
| Step 6 |
Check that all services are running on the remaining two nodes: magctl node display magctl appstack status |
Add a Replacement Node
After removing the failed node, you can add a replacement node to the cluster.
Before you begin
Make sure that you complete the following tasks:
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Remove the failed node. For information, see Remove the Failed Node.
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Allocate at least 30 minutes to perform this procedure.
Procedure
| Step 1 |
On the replacement node, install the same software version that the other nodes in the cluster are running.
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| Step 2 |
After the installation is complete, enter the following command: magctl node display The replacement node should show the Ready status. |
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| Step 3 |
Redistribute services to the replacement node by activating high availability on your cluster:
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| Step 4 |
Verify that services have been redistributed: magctl appstack status The replacement node should show a Running status. |
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| Step 5 |
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.
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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:
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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.
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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.
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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:
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Software
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Network access
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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.
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Requires User Action |
Failure Scenario |
HA Behavior |
|---|---|---|
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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. |
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No |
A node fails, is unreachable, or experiences a service failure for less than 5 minutes. |
After the node is restored:
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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:
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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:
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Yes |
Two nodes fail or are unreachable. |
The cluster is broken and the UI is not accessible until connectivity has been restored.
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Yes |
A node fails and needs to be removed from a cluster. |
Complete the tasks described in Recover a Failed Cluster Node to remove and then restore a failed cluster node. |
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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. |
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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. |
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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:
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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. |
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Yes |
A failure occurs while upgrading a cluster. |
Contact the Cisco TAC for assistance. |
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No |
An appliance port fails. |
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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. |
Explanation of Pending State During a Failover
A pod that is in Pending state behaves as follows:
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Stateful set: The pod has some type of data storage. These pods are node bound using local persistent volume (LPV)—when the node is down, all stateful sets on that node move to Pending state. Stateful examples are Mongodb, Elasticsearch, and Postgres.
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DaemonSet: By design, the pod is strictly node bound. DaemonSet examples are agent, broker-agent, and keepalived.
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Stateless/deployment:
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While the pod doesn’t have a data to store of its own, it uses a stateful set to store and/or retrieve data.
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Deployment scale varies. Some deployments have 1x pod instance (such as spf-service-manager-service); some have 2x pod instances (such as apic-em-inventory-manager-service); some have 3x pod instances (such as kong, platform-ui, collector-snmp).
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The 1x stateless pods are free to move across nodes based on the current state of the cluster.
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The 2x stateless pods have flexibility to move across nodes, but no two instances of stateless pods can run on the same node.
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The 3x stateless pods have node anti-affinity, meaning no two instances can run on the same node.
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