# eredis_cluster (Nordix fork)
eredis_cluster is a wrapper for eredis to support cluster mode of Redis 3.0.0+
[](https://github.com/Nordix/eredis_cluster)
[](https://hex.pm/packages/eredis_cluster)
[](https://hex.pm/packages/eredis_cluster)
## Contents
* [Improvements compared to adrienmo/eredis_cluster](#improvements-compared-to-adrienmoeredis_cluster)
* [Usage](#usage)
* [Compilation and tests](#compilation-and-tests)
* [Configuration](#configuration)
* [Troubleshooting](#troubleshooting)
* [See also](#see-also)
## Improvements compared to `adrienmo/eredis_cluster`
* Support of TLS introduced in Redis 6
* Uses [Nordix/eredis](https://github.com/Nordix/eredis) (TLS, error handling fixes)
* Many Dialyzer corrections
* Elvis code formatting
* Optimizations
* Refresh slot mapping reuses existing connection when
possible and don't refresh mapping when not needed, e.g. when a pool is busy
* Don't use an extra wrapper process around each eredis connection process
* Containerized testing
* Testing using [simulated Redis cluster](https://github.com/Nordix/fakeredis_cluster) for corner cases such as ASK redirects
* Added API functions:
- `connect/2`: Connect to init nodes, with options
- `qa2/1`: Query all nodes with re-attempts, returns
`[{Node, Result}, ...]`
- `qn/2`: Query to specific Redis node
- `q_noreply/1`: Query a single Redis node but wont wait for its result
- `load_script/1`: Pre-load script to all Redis nodes
- `scan/4`: Perform a scan command on given Redis nodes
- `disconnect/1`: Disconnect from given Redis node
- `get_all_pools/0`: Get all pools (one for each Redis node in cluster)
- `get_pool_by_command/1`: Get which Redis pool that handles a given command
- `get_pool_by_key/1`: Get which Redis pool that handles a given key
- `eredis_cluster_monitor:get_cluster_nodes/0`: Get cluster nodes information
list (CLUSTER NODES)
- `eredis_cluster_monitor:get_cluster_slots/0`: Get cluster slots information
(CLUSTER SLOTS)
* Changed behaviour:
- `qa/1`: Query all nodes, now with re-attempts
- `transaction/2`: The second argument can be a Redis node (pool) or
a key, instead of only a key
## Usage
For the full reference manual, see the generated documentation in
[doc/eredis_cluster.md](doc/eredis_cluster.md).
Published documentation can also be found on [hexdocs](https://hexdocs.pm/eredis_cluster/).
```erlang
%% Start the application and, if init nodes are defined in the application
%% configuration, connect to the cluster (otherwise use connect/1,2)
eredis_cluster:start().
%% Simple command
eredis_cluster:q(["GET","abc"]).
%% Pipeline
eredis_cluster:qp([["LPUSH", "a", "a"], ["LPUSH", "a", "b"], ["LPUSH", "a", "c"]]).
%% Pipeline in multiple node (keys are sorted by node, a pipeline request is
%% made on each node, then the result is aggregated and returned. The response
%% keep the command order
eredis_cluster:qmn([["GET", "a"], ["GET", "b"], ["GET", "c"]]).
%% Transaction
eredis_cluster:transaction([["LPUSH", "a", "a"], ["LPUSH", "a", "b"], ["LPUSH", "a", "c"]]).
%% Transaction Function
Function = fun(Worker) ->
eredis_cluster:qw(Worker, ["WATCH", "abc"]),
{ok, Var} = eredis_cluster:qw(Worker, ["GET", "abc"]),
%% Do something with Var %%
Var2 = binary_to_integer(Var) + 1,
{ok, Result} = eredis_cluster:qw(Worker,[["MULTI"], ["SET", "abc", Var2], ["EXEC"]]),
lists:last(Result)
end,
eredis_cluster:transaction(Function, "abc").
%% Optimistic Locking Transaction
Function = fun(GetResult) ->
{ok, Var} = GetResult,
Var2 = binary_to_integer(Var) + 1,
{[["SET", Key, Var2]], Var2}
end,
Result = optimistic_locking_transaction(Key, ["GET", Key], Function),
{ok, {TransactionResult, CustomVar}} = Result.
%% Atomic Key update
Fun = fun(Var) -> binary_to_integer(Var) + 1 end,
eredis_cluster:update_key("abc", Fun).
%% Atomic Field update
Fun = fun(Var) -> binary_to_integer(Var) + 1 end,
eredis_cluster:update_hash_field("abc", "efg", Fun).
%% Load LUA script on all nodes
Script = "return redis.call('set', KEYS[1], ARGV[1]);",
{ok, ScriptHash} = eredis_cluster:load_script(Script),
%% Execute pre-loaded script based on hash (EVALSHA) on the node where
%% the key "abs" is, with a fallback to load it if needed.
eredis_cluster:eval(Script, ScriptHash, ["abc"], ["123"]).
%% Flush DB
eredis_cluster:flushdb().
%% Query on all cluster server
eredis_cluster:qa(["FLUSHDB"]).
%% Execute a query on the server containing the key "TEST"
eredis_cluster:qk(["FLUSHDB"], "TEST").
```
## Compilation and tests
The directory contains a Makefile that uses rebar3.
Setup a Redis cluster and start the tests using following commands:
```bash
make # ... or rebar3 compile
make start # Start a local Redis cluster using Docker
make test # Run tests towards the cluster
make stop # Teardown the Redis cluster
```
## Configuration
To configure the Redis cluster client, you can use an application variable
(probably in your app.config):
{eredis_cluster,
[
{init_nodes,[
{"127.0.0.1", 30001},
{"127.0.0.1", 30002}
]},
{pool_size, 5},
{pool_max_overflow, 10},
{password, "redis_pw"},
{socket_options, [{send_timeout, 6000}, ...]},
{tls, [{cacertfile, "ca.crt"}, ...]}
]
}
You don't need to specify all nodes of your configuration as eredis_cluster will
retrieve them through the command `CLUSTER SLOTS` at runtime.
### Configuration parameters
* `init_nodes`: List of Redis nodes to fetch cluster information from. Default: `[]`
* `pool_size`: Number of connected clients to each Redis node. Default: `10`
* `pool_max_overflow`: Max number of extra clients that can be started when the pool is exhausted. Default: `0`
* `password`: Password to use for a Redis cluster configured with `requirepass`. Default: `""` (i.e. AUTH not sent)
* `socket_options`: Extra socket [options](http://erlang.org/doc/man/gen_tcp.html#type-option). Enables selecting host interface or perf. tuning. Default: `[]`
* `tls`: Enable TLS/SSL and use specified [TLSOptions](https://erlang.org/doc/man/ssl.html#type-client_option). Default: TLS not enabled.
### Configuring via API
An alternative is to set configurations programmatically via set_env() and `eredis_cluster:connect/1`.
```erlang
application:set_env(eredis_cluster, pool_size, 5),
application:set_env(eredis_cluster, pool_max_overflow, 10),
application:set_env(eredis_cluster, password, "redis_pw"),
application:set_env(eredis_cluster, socket_options, [{send_timeout, 6000}]),
application:set_env(eredis_cluster, tls, [{cacertfile, "ca.crt"},
{certfile, "client.crt"},
{keyfile, "client.key"}]),
%% Set initial nodes and perform a controlled connect
eredis_cluster:connect([{"127.0.0.1", 30001},
{"127.0.0.1", 30002}]).
```
### Configuring using connect/2
It is also possible to give options while doing a connect using `eredis_cluster:connect/2`.
The given options will override options set via application configuration,
i.e will be prepended to the property list.
```erlang
Options = [{tls, [{cacertfile, "ca.crt"},
{certfile, "client.crt"},
{keyfile, "client.key"}]}],
eredis_cluster:connect([{"127.0.0.1", 30001},
{"127.0.0.1", 30002}], Options).
```
## Troubleshooting
The following Redis-log indicates that Redis accepts TLS, but the client is not configured for TLS.
```
# Error accepting a client connection: error:1408F10B:SSL routines:ssl3_get_record:wrong version number (conn: fd=12)
```
Debug logging for TLS connections can be enabled in eredis_cluster by the connect option: `{log_level, debug}`
## See also
* Generated documentation: [doc/eredis_cluster.md](doc/eredis_cluster.md)
* Dependencies:
* [Poolboy](https://github.com/devinus/poolboy)
* [Eredis](https://github.com/Nordix/eredis)
