Configuring Cluster DNS
DNS is critical to the default operation of Redis Enterprise Software (RS) deployments. This can be altered, but instead using the Discovery Service, which utilizes pure IP based connectivity as it is compliant with the Redis Sentinel API.
As part of the high availability capabilities in RS, each node includes a small DNS server for managing various internal cluster functionalities, such as automatic failover or automatic migration. Therefore, the node on which you are provisioning RS should not run any other DNS server except for the one included with the RS installation. The existence of another DNS server on the same machine might cause unexpected and erroneous behavior.
Cluster name (FQDN) and connection management
When connecting to the cluster for administration or connecting to databases for data access, there are 2 options:
- URL Based Connections: URL based connections require DNS setup for resolution of the cluster name (FQDN) when connecting to the cluster for administration or connecting to databases for data access. As the topology of the cluster changes and new nodes are added or existing nodes are removed from the cluster, DNS records may need to be modified. However, with URL based connections, applications simply have to remember the URL for the cluster or the database.
- IP Based Connections: IP based connections do not require DNS setup and instead use IP addresses of the nodes in the cluster for connecting to the cluster for administration or data access. As the topology of the cluster changes and new nodes are added or existing nodes are removed from the cluster, no DNS records need to be modified. However, administrators and applications connecting to the cluster and to the databases need to maintain IP address of at least one node in the cluster to discover and access the cluster topology.
URL-based connections and how to set up cluster name (FQDN)
The Fully Qualified Domain Name (FQDN) is the unique cluster identifier that enables clients to connect to the different components that are part of the Redis Enterprise Software (RS). The FQDN is a crucial component of the high-availability mechanism in RS because it is used by the internal DNS to enable the automatic and transparent failover of nodes, databases shards, and endpoints, by automatically updating their IP addresses.
Note: Setting the cluster’s FQDN is a one-time operation. Once the FQDN is set it cannot be updated.
Naming the cluster FQDN
You have two options for naming the cluster FQDN:
Use this option if you already have your own domain, would like to make the cluster part of your domain and are able to update the DNS.
Make sure that the cluster and at least one node (preferably all nodes) in the cluster are correctly configured in the DNS with the appropriate NS entries.
- Your domain is: mydomain.com - You would like to name the Redis Enterprise Software cluster: redislabscluster - You have three nodes in the cluster: - node1 with IP 220.127.116.11 - node2 with IP 18.104.22.168 - node3 with IP 22.214.171.124
In the FQDN field, enter the value: redislabscluster.mydomain.com, and add the following records in the DNS for mydomain.com:
redislabscluster.mydomain.com NS node1.redislabscluster.mydomain.com node2.redislabscluster.mydomain.com node3.redislabscluster.mydomain.com node1.redislabscluster.mydomain.com A 126.96.36.199 node2.redislabscluster.mydomain.com A 188.8.131.52 node3.redislabscluster.mydomain.com A 184.108.40.206
Zero-configuration using mDNS (Development option only)
Note: mDNS is not supported for use with production environments and should only be used in dev/test environments.
mDNS (Multicast DNS) is a standard protocol that provides DNS-like name resolution and service discovery capabilities to machines on local networks with minimal to no configuration. Because not all clients support mDNS, ensure first that the clients that are connecting to the cluster actually have mDNS support, and that the network infrastructure permits mDNS / multi-casting between them and the cluster nodes.
Configuring the cluster to support mDNS requires you to assign the cluster a .local name.
For example, if you want to name the Redis Enterprise Software cluster: redislabscluster
- In the FQDN field, enter the value: redislabscluster.local
When using the DNS or mDNS option, failover can be done transparently and the DNS is updated automatically to point to the IP of the new master.
When you use IP based connection option, the FQDN does not need to have any special format because clients use IP addresses instead of hostnames to access the databases so you are free to choose whatever name you want. Using the IP Based connection option does not require any DNS configuration either.
To administer the cluster you do need to know the IP address of at least one of the nodes in the cluster. Once you have the IP address, you can simply connect to port number 8443 (for example: https://10.0.0.12:8443). However, as the topology of the cluster changes and node with the given IP address is removed, you need to remember the IP address of another node participating in this cluster to connect to the admin console and manage the cluster.
Applications connecting to RS databases for data access have the same constraints. When using the IP based connection method, you can use the Discovery Service to discover the database endpoint for a given database name as long as you have an IP address for at least one of the nodes in the cluster. The API used for discovery service is compliant with the Redis Sentinel API.
You can find examples of how to connect to databases using the DNS or IP based methods from various client libraries here on the How-To page.
You can find a simple example of URL and IP Based connection in the “Testing Connectivity to your Database” section on the “Creating a new database” page.