What is Redis Sentinel?

What is Redis Sentinel?

Redis Sentinel is the high-availability solution for open-source Redis server. It provides monitoring of all Redis nodes and automatic failover should the master node become unavailable. This guide provides a sample configuration for a three-node Redis cluster.

Why use Redis Sentinel?

Redis Sentinel is a monitoring solution for Redis instances that handles automatic failover of Redis masters and service discovery (who is the current master for a given group of instances?). Improved safety of Redis Sentinel automatic failover.

How does Redis Sentinel work?

Sentinel acts as a source of authority for clients service discovery: clients connect to Sentinels in order to ask for the address of the current Redis master responsible for a given service. If a failover occurs, Sentinels will report the new address.

What is the difference between Redis cluster and Sentinel?

Redis Sentinel is the name of the Redis high availability solution… It has nothing to do with Redis Cluster and is intended to be used by people that don’t need Redis Cluster, but simply a way to perform automatic fail over when a master instance is not functioning correctly.

Can Redis have multiple masters?

You can deploy as many masters as you want, with any number of slaves each, but they will behave like a single separated cluster with their own memory space, and it will be your responsibility at the application layer to spread your keys properly using each of the masters, just as you would do in a Memcached multi-node …

Is Redis single point of failure?

A Redis cluster is simply a data sharding strategy. It automatically partitions data across multiple Redis nodes. It is an advanced version of Redis that achieves distributed storage and prevents a single point of failure.

How do I know if Redis Sentinel is running?

You can also use monitor to see what Sentinel is doing: $ redis-cli -p 6379 monitor OK 1546981642.808843 [0 127.0. 0.1:54765] “PING” 1546981642.866671 [0 127.0. 0.1:54765] “PUBLISH” “__sentinel__:hello” “127.0.

Is Redis single threaded?

Redis is, mostly, a single-threaded server from the POV of commands execution (actually modern versions of Redis use threads for different things). It is not designed to benefit from multiple CPU cores. People are supposed to launch several Redis instances to scale out on several cores if needed.

What is a shard in Redis?

A shard (API/CLI: node group) is a collection of one to six Redis nodes. A Redis (cluster mode disabled) cluster will never have more than one shard. You can create a cluster with higher number of shards and lower number of replicas totaling up to 90 nodes per cluster.

Is Redis highly available?

High availability in Redis is achieved through master-slave replication. However, the most common HA solution that comes bundled with Redis is Redis Sentinels. Redis Sentinels run as a set of separate processes that in combination monitor Redis master-slave sets and provide automatic failover and reconfiguration.

What is Redis architecture?

Redis employs a primary-replica architecture and supports asynchronous replication where data can be replicated to multiple replica servers. This provides improved read performance (as requests can be split among the servers) and faster recovery when the primary server experiences an outage.

How do I reset my Sentinel?

In the Control Panel, open Administrative Tools. Double-‐click Services. Select the Sentinel LDK License Manager service in the list. If it stops, Right-‐click the service and select Start or Restart from the context menu.

What do you need to know about Redis Sentinel?

Redis Sentinel provides high availability for Redis. In practical terms this means that using Sentinel you can create a Redis deployment that resists without human intervention certain kinds of failures. Redis Sentinel also provides other collateral tasks such as monitoring, notifications and acts as a configuration provider for clients.

What happens in Redis in case of a failure?

Redis sentinel is the high availability solution offered by Redis. In case of a failure in your Redis cluster, Sentinel will automatically detects the point of failure and bring the cluster back to stable mode without any human intervention. What really happens inside Redis Sentinel?

Which is the best HA solution for Redis?

Redis Sentinel provides a simple and automatic high availability (HA) solution for Redis. If you’re familiar with how MongoDB elections work, this isn’t too far off. To start, you have a given master replicating to N number of slaves.

Why did the + sdown event happen after Redis went away?

The +sdown event happened 5 seconds after Redis went away; this is due to the sentinel down-after-milliseconds mymaster 5000 config that we set earlier. Sentinel detected that Redis went away, but it didn’t actually do anything in response.