Redis

Envoy can act as a Redis proxy, partitioning commands among instances in a cluster. In this mode, the goals of Envoy are to maintain availability and partition tolerance over consistency. This is the key point when comparing Envoy to Redis Cluster. Envoy is designed as a best-effort cache, meaning that it will not try to reconcile inconsistent data or keep a globally consistent view of cluster membership. It also supports routing commands from different workloads to different upstream clusters based on their access patterns, eviction, or isolation requirements.

The Redis project offers a thorough reference on partitioning as it relates to Redis. See “Partitioning: how to split data among multiple Redis instances”.

Features of Envoy Redis:

• Redis protocol codec.

• Hash-based partitioning.

• Redis transaction support.

• Ketama distribution.

• Detailed command statistics.

• Active and passive healthchecking.

• Hash tagging.

• Prefix routing.

• Separate downstream client and upstream server authentication.

• Request mirroring for all requests or write requests only.

• Control read requests routing. This only works with Redis Cluster.

Planned future enhancements:

• Additional timing stats.

• Circuit breaking.

• Request collapsing for fragmented commands.

• Replication.

• Built-in retry.

• Tracing.

Configuration

For filter configuration details, see the Redis proxy filter configuration reference.

The corresponding cluster definition should be configured with ring hash load balancing.

If active health checking is desired, the cluster should be configured with a custom health check which configured as a Redis health checker.

If passive healthchecking is desired, also configure outlier detection.

For the purposes of passive healthchecking, connect timeouts, command timeouts, and connection close map to 5xx. All other responses from Redis are counted as a success.

Redis Cluster Support

Envoy offers support for Redis Cluster.

When using Envoy as a sidecar proxy for a Redis Cluster, the service can use a non-cluster Redis client implemented in any language to connect to the proxy as if it’s a single node Redis instance. The Envoy proxy will keep track of the cluster topology and send commands to the correct Redis node in the cluster according to the spec. Advance features such as reading from replicas can also be added to the Envoy proxy instead of updating redis clients in each language.

Envoy proxy tracks the topology of the cluster by sending periodic cluster slots commands to a random node in the cluster, and maintains the following information:

• List of known nodes.

• The primaries for each shard.

• Nodes entering or leaving the cluster.

Envoy proxy supports identification of the nodes via both IP address and hostnames in the cluster slots command response. In case of failure to resolve a primary hostname, Envoy will retry resolution of all nodes periodically until success. Failure to resolve a replica simply skips that replica. On the other hand, if the enable_redirection option is set and a MOVED or ASK response containing a hostname is received Envoy will not automatically do a DNS lookup and instead bubble the error to the client verbatim. To have Envoy do the DNS lookup and follow the redirection, you need to configure the DNS cache option dns_cache_config under the connection pool settings. For a configuration example on how to enable DNS lookups for redirections, see the filter configuration reference.

For topology configuration details, see the Redis Cluster v3 API reference.

Every Redis cluster has its own extra statistics tree rooted at cluster.<name>.redis_cluster. with the following statistics:

Name	Type	Description
max_upstream_unknown_connections_reached	Counter	Total number of times that an upstream connection to an unknown host is not created after redirection having reached the connection pool’s max_upstream_unknown_connections limit
upstream_cx_drained	Counter	Total number of upstream connections drained of active requests before being closed
upstream_commands.upstream_rq_time	Histogram	Histogram of upstream request times for all types of requests

Per-cluster command statistics can be enabled via the setting enable_command_stats.:

Name	Type	Description
upstream_commands.[command].success	Counter	Total number of successful requests for a specific Redis command
upstream_commands.[command].failure	Counter	Total number of failed or cancelled requests for a specific Redis command
upstream_commands.[command].total	Counter	Total number of requests for a specific Redis command (sum of success and failure)
upstream_commands.[command].latency	Histogram	Latency of requests for a specific Redis command

Transactions

Transactions (MULTI) are supported. Their use is no different from regular Redis: you start a transaction with MULTI, and you execute it with EXEC. Within the transaction only commands that are supported by Envoy (see below) and are single-key commands are supported, i.e. MGET and MSET are not supported. The DISCARD command is supported.

When working in Redis Cluster mode, Envoy will relay all the commands in the transaction to the node handling the first key-based command in the transaction. It is the user’s responsibility to ensure that all keys in the transaction are mapped to the same hashslot, as commands will not be redirected.

Supported commands

At the protocol level, pipelines are supported. Use pipelining wherever possible for the best performance.

At the command level, Envoy only supports commands that can be reliably hashed to a server. AUTH and PING are the only exceptions. AUTH is processed locally by Envoy if a downstream password has been configured, and no other commands will be processed until authentication is successful when a password has been configured. Envoy will transparently issue AUTH commands upon connecting to upstream servers, if upstream authentication passwords are configured for the cluster. Envoy responds to PING immediately with PONG. Arguments to PING are not allowed. All other supported commands must contain a key. Supported commands are functionally identical to the original Redis command except possibly in failure scenarios.

For details on each command’s usage see the official Redis command reference.

Command	Group
AUTH	Authentication
PING	Connection
QUIT	Connection
DEL	Generic
DISCARD	Transaction
DUMP	Generic
EXEC	Transaction
EXISTS	Generic
EXPIRE	Generic
EXPIREAT	Generic
PERSIST	Generic
PEXPIRE	Generic
PEXPIREAT	Generic
PTTL	Generic
RESTORE	Generic
TOUCH	Generic
TTL	Generic
TYPE	Generic
UNLINK	Generic
GEOADD	Geo
GEODIST	Geo
GEOHASH	Geo
GEOPOS	Geo
GEORADIUS_RO	Geo
GEORADIUSBYMEMBER_RO	Geo
HDEL	Hash
HEXISTS	Hash
HGET	Hash
HGETALL	Hash
HINCRBY	Hash
HINCRBYFLOAT	Hash
HKEYS	Hash
HLEN	Hash
HMGET	Hash
HMSET	Hash
HSCAN	Hash
HSET	Hash
HSETNX	Hash
HSTRLEN	Hash
HVALS	Hash
PFADD	HyperLogLog
PFCOUNT	HyperLogLog
LINDEX	List
LINSERT	List
LLEN	List
LPOP	List
LPUSH	List
LPUSHX	List
LRANGE	List
LREM	List
LSET	List
LTRIM	List
MULTI	Transaction
RPOP	List
RPUSH	List
RPUSHX	List
EVAL	Scripting
EVALSHA	Scripting
SADD	Set
SCARD	Set
SISMEMBER	Set
SMEMBERS	Set
SPOP	Set
SRANDMEMBER	Set
SREM	Set
SSCAN	Set
WATCH	String
ZADD	Sorted Set
ZCARD	Sorted Set
ZCOUNT	Sorted Set
ZINCRBY	Sorted Set
ZLEXCOUNT	Sorted Set
ZRANGE	Sorted Set
ZRANGEBYLEX	Sorted Set
ZRANGEBYSCORE	Sorted Set
ZRANK	Sorted Set
ZREM	Sorted Set
ZREMRANGEBYLEX	Sorted Set
ZREMRANGEBYRANK	Sorted Set
ZREMRANGEBYSCORE	Sorted Set
ZREVRANGE	Sorted Set
ZREVRANGEBYLEX	Sorted Set
ZREVRANGEBYSCORE	Sorted Set
ZREVRANK	Sorted Set
ZPOPMIN	Sorted Set
ZPOPMAX	Sorted Set
ZSCAN	Sorted Set
ZSCORE	Sorted Set
APPEND	String
BITCOUNT	String
BITFIELD	String
BITPOS	String
DECR	String
DECRBY	String
GET	String
GETBIT	String
GETDEL	String
GETRANGE	String
GETSET	String
INCR	String
INCRBY	String
INCRBYFLOAT	String
MGET	String
MSET	String
PSETEX	String
SET	String
SETBIT	String
SETEX	String
SETNX	String
SETRANGE	String
STRLEN	String

Failure modes

If Redis throws an error, we pass that error along as the response to the command. Envoy treats a response from Redis with the error datatype as a normal response and passes it through to the caller.

Envoy can also generate its own errors in response to the client.

Error	Meaning
no upstream host	The ring hash load balancer did not have a healthy host available at the ring position chosen for the key.
upstream failure	The backend did not respond within the timeout period or closed the connection.
invalid request	Command was rejected by the first stage of the command splitter due to datatype or length.
unsupported command	The command was not recognized by Envoy and therefore cannot be serviced because it cannot be hashed to a backend server.
finished with n errors	Fragmented commands which sum the response (e.g. DEL) will return the total number of errors received if any were received.
upstream protocol error	A fragmented command received an unexpected datatype or a backend responded with a response that not conform to the Redis protocol.
wrong number of arguments for command	Certain commands check in Envoy that the number of arguments is correct.
NOAUTH Authentication required.	The command was rejected because a downstream authentication password has been set and the client has not successfully authenticated.
ERR invalid password	The authentication command failed due to an invalid password.
ERR Client sent AUTH, but no password is set	An authentication command was received, but no downstream authentication password has been configured.

In the case of MGET, each individual key that cannot be fetched will generate an error response. For example, if we fetch five keys and two of the keys’ backends time out, we would get an error response for each in place of the value.

$ redis-cli MGET a b c d e
1) "alpha"
2) "bravo"
3) (error) upstream failure
4) (error) upstream failure
5) "echo"