moonlibs/config

Package for loading external lua config

Config

Module to make proper initialization and configuration of tarantool instance.

It can be used with or without ETCD.

Only ETCD APIv2 now supported.

• Config
  • Status
  • Installation
  • Configuration
    • Example of conf.lua
    • Usage in init.lua
  • Usage
  • Topologies
    • Single-shard topology
      • Example of init.lua
      • Example of /etc/userdb/conf.lua
      • Example of ETCD configuration (etcd.cluster.master)
        • Configuration precedence
      • Fencing configuration
      • Fencing algorithm
    • Operations during disaster
    • Multi-proxy topology (etcd.instance.single)
      • Example of proxy init.lua
      • Example of /etc/proxy/conf.lua
      • Example of ETCD configuration (etcd.instance.single)
    • Multi-shard topology for custom sharding (etcd.cluster.master)
    • Multi-shard topology for vshard-based applications (etcd.cluster.vshard)
      • Example of ETCD configuration for vshard-based applications (etcd.cluster.vshard)
      • Example of vshard-based init.lua (etcd.cluster.vshard)
      • VShard Maintenance

Status

Ready for production use.

Latest stable release: config 0.7.1.

Installation

tarantoolctl rocks --server=https://moonlibs.org install config 0.7.1

Starting with Tarantool 2.10.0 you may add configuration of moonlibs.org into config-5.1.lua

$ cat .rocks/config-5.1.lua
rocks_servers = {
   "https://moonlibs.org",
   "http://moonlibs.github.io/rocks",
   "http://rocks.tarantool.org/",
   "http://luarocks.org/repositories/rocks"
}

Configuration

To configure tarantool instance you must deploy conf.lua file.

Example of conf.lua

Typically conf.lua should be located in /etc/<app-name>/conf.lua.

assert(instance_name, "instance_name must be defined")
etcd = {
    instance_name = instance_name,
    prefix = '/etcd/path/to/application/etcd',
    endpoints = {
        "https://etcd1:2379",
        "https://etcd2:2379",
        "https://etcd3:2379",
    },
    timeout = 3,
    boolean_auto = true,
    print_config = true,
    login = 'etcd-username',
    password = 'etcd-password',
}

-- This options will be passed as is to box.cfg
box = {
    pid_file  = '/var/run/tarantool/'..instance_name..'.pid',
    memtx_dir = '/var/lib/tarantool/snaps/' .. instance_name,
    wal_dir   = '/var/lib/tarantool/xlogs/' .. instance_name,
    log_nonblock = false,
}

--- You may hardcode options for your application in `app` section
app = {

}

Usage in init.lua

local instance_name = os.getenv('TT_INSTANCE_NAME')

require 'config' {
    mkdir = true,
    instance_name = instance_name,
    file = '/etc/<app-name>/conf.lua',
    master_selection_policy = 'etcd.cluster.master',
}

print("Tarantool bootstrapped")

Usage

Module config is used both for bootstrap and configuration of your Tarantool application.

In application you may access config options using following syntax

local DEFAULT_TIMEOUT = 3

--- If app/http/timeout is defined in config (ETCD or conf.lua) then it will be returned
--- otherwise value of DEFAULT_TIMEUOT will be returned
local http_timeout = config.get('app.http.timeout', DEFAULT_TIMEOUT)

--- If app/is_enabled is not defined then `nil` will be returned.
local is_enabled = config.get('app.is_enabled')

Topologies

moonlibs/config supports different types of Tarantool topologies.

All of them make sence when application is configured using ETCD.

To distinguish application topology option master_selection_policy is used.

Single-shard topology

In most cases you need single shard topology. It means, that your application has single master and many replicas.

Shard will be configured with full-mesh topology. Read more about full-mesh topology on Tarantool website.

Each instance of application must have unique name. For example:

• userdb_001
• userdb_002
• userdb_003

Typically instance name should not contain master or replica word in it.

Example of init.lua

--- variable instance_name must be derived somehow for each tarantool instance
--- For example from name of the file. or from environment variable
require 'config' {
    mkdir = true,
    instance_name = instance_name,
    file = '/etc/userdb/conf.lua',
    master_selection_policy = 'etcd.cluster.master',
}

Example of /etc/userdb/conf.lua

assert(instance_name, "instance_name must be defined")
etcd = {
    instance_name = instance_name,
    prefix = '/tarantool/userdb',
    endpoints = {
        "https://etcd1:2379",
        "https://etcd2:2379",
        "https://etcd3:2379",
    },
    timeout = 3,
    boolean_auto = true,
    print_config = true,
}

-- This options will be passed as is to box.cfg
box = {
    pid_file  = '/var/run/tarantool/'..instance_name..'.pid',
    memtx_dir = '/var/lib/tarantool/snaps/' .. instance_name,
    wal_dir   = '/var/lib/tarantool/xlogs/' .. instance_name,
    log_nonblock = false,
}

Example of ETCD configuration (etcd.cluster.master)

tarantool:
  userdb:
    clusters:
      userdb:
        master: userdb_001
        replicaset_uuid: 045e12d8-0001-0000-0000-000000000000
    common:
      box:
        log_level: 5
        memtx_memory: 268435456
    instances:
      userdb_001:
        cluster: userdb
        box:
          instance_uuid: 045e12d8-0000-0001-0000-000000000000
          listen: 10.0.1.11:3301
      userdb_002:
        cluster: userdb
        box:
          instance_uuid: 045e12d8-0000-0002-0000-000000000000
          listen: 10.0.1.12:3302
      userdb_003:
        cluster: userdb
        box:
          instance_uuid: 045e12d8-0000-0003-0000-000000000000
          listen: 10.0.1.13:3303

/tarantool/userdb -- is root path for application configuration

/tarantool/userdb/common -- is common configuration for each instance of application.

/tarantool/userdb/common/box -- is section to configure box.cfg parameters. See more on Tarantool website.

/tarantool/userdb/clusters section contains list of shards. For single-shard application it is good to single shard it as application itself.

/tarantool/userdb/instances section contains instance-specific configuration. It must contain /box/{listen,instance_uuid} and cluster options.

Configuration precedence

• /etc/app-name/conf.lua
• ETCD:/instances/<instance_name>
• ETCD:/common/
• config.get default value

Fencing configuration

etcd.cluster.master topology supports auto fencing mechanism.

Auto fencing is implemented via background fiber which waits for changes on <prefix>/clusters/<my-shard-name> directory.

fencing_pause must be less than fencing_timeout. The fencing_timeout - fencing_pause time slot is used to retry ETCD (at least 2 attempts with sleeps in between) to ensure that ETCD is really down.

You may increase fencing_pause if you see that too many requests is made to ETCD. If fencing_timeout - fencing_pause is too small (less than etcd/timeout) then you may face False-Positive fencing when ETCD was slightly down.

Increasing fencing_timeout will decrease possibility of False Positive fencing.

You leader will be RW at least fencing_timeout if everyone else is down.

There are 4 parameters to configure:

Parameter	Description	Default Value
etcd/fencing_enabled	Trigger to enable/disable fencing	false
etcd/fencing_timeout	Fencing timeout	10 (seconds)
etcd/fencing_pause	Fencing pause	fencing_timeout/2
etcd/fencing_check_replication	Respect replication when ETCD is down	false

Example of enabled fencing:

tarantool:
  userdb:
    common:
      etcd:
        fencing_enabled: true

Fencing also can be enabled in conf.lua:

etcd = {
    endpoints = {"http://etcd1:2379", "http://etcd2:2379", "http://etcd3:2379"},
    prefix = "/tarantool/userdb",
    timeout = 3,
    fencing_enabled = true,
}

Fencing algorithm

Fencing can be enabled only for topology etcd.cluster.master and only if etcd/fencing_enabled is true (default: false).

Fencing algorithm is the following:

0. Wait until instance became rw.
1. Wait randomized (fencing_timeout - fencing_pause) / 10.
2. Recheck ETCD <prefix>/clusters/<my-shard-name> in fencing_pause.
3. Depends on response:
   1. [ETCD is ok] => provision self to be rw for next fencing_timeout seconds. Go to 1.
   2. [ETCD is down] => execute box.cfg{read_only=true} if etcd/fencing_check_replication is disabled. Go to 0.
   3. [ETCD has another master, and switching in progress] => do nothing. Go to 1.
   4. [ETCD has another master, and switching is not in progress] => execute box.cfg{read_only=true}. Go to 0.

Note: to request ETCD Quorum Reads are used. So it is safe to use it in split brain.

Operations during disaster

When ETCD failed to determine leader cluster can't reload it's configuration (or restart).

During disaster, you must recovery ETCD elections mechanism first.

If it is not possible, and you need to reload configuration or restart instance you may switch to manual configuration mode.

To do that set reduce_listing_quorum to true in conf.lua config.

After ETCD becames operation you must remove this option from local configuration.

etcd = {
  reduce_listing_quorum = true,
}

Enabling this option automatically disables fencing.

Be extra careful to not allow Tarantool Master-Master setup. (Since ETCD may have different configuration on it's replicas).

Multi-proxy topology (etcd.instance.single)

moonlibs/config supports multi proxy topology. This topology is usefull when you need to have many stateless tarantool proxies or totally independent masters.

Each instance should have unique name. For example:

• proxy_001
• proxy_002
• proxy_003
• proxy_004
• proxy_005

Example of proxy init.lua

--- variable instance_name must be derived somehow for each tarantool instance
--- For example from name of the file. or from environment variable
require 'config' {
    mkdir = true,
    instance_name = instance_name,
    file = '/etc/proxy/conf.lua',
    master_selection_policy = 'etcd.instance.single',
}

Example of /etc/proxy/conf.lua

assert(instance_name, "instance_name must be defined")
etcd = {
    instance_name = instance_name,
    prefix = '/tarantool/proxy',
    endpoints = {
        "https://etcd1:2379",
        "https://etcd2:2379",
        "https://etcd3:2379",
    },
    timeout = 3,
    boolean_auto = true,
    print_config = true,
}

-- This options will be passed as is to box.cfg
box = {
    pid_file  = '/var/run/tarantool/'..instance_name..'.pid',
    memtx_dir = '/var/lib/tarantool/snaps/' .. instance_name,
    wal_dir   = '/var/lib/tarantool/xlogs/' .. instance_name,
    log_nonblock = false,
}

Example of ETCD configuration (etcd.instance.single)

tarantool:
  proxy:
    common:
      box:
        log_level: 5
        memtx_memory: 33554432
    instances:
      proxy_001:
        box:
          instance_uuid: 01712087-0000-0001-0000-000000000000
          listen: 10.0.2.12:7101
      proxy_002:
        box:
          instance_uuid: 01712087-0000-0002-0000-000000000000
          listen: 10.0.2.13:7102
      proxy_003:
        box:
          instance_uuid: 01712087-0000-0003-0000-000000000000
          listen: 10.0.2.11:7103

The etcd configuration is the same as etcd.cluster.master except that /tarantool/proxy/clusters is not defined.

Also /tarantool/proxy/instances/<instance-name>/cluster must not be defined.

Multi-shard topology for custom sharding (etcd.cluster.master)

etcd.cluster.master can be used for multi-shard topologies as well.

Multi-shard means that application consists of several replicasets. Each replicaset has single master and several replicas.

conf.lua and init.lua files remains exactly the same. But configuration of ETCD slightly changes:

tarantool:
  notifications:
    clusters:
      notifications_002:
        master: notifications_002_01
        replicaset_uuid: 11079f9c-0002-0000-0000-000000000000
      notifications_001:
        master: notifications_001_01
        replicaset_uuid: 11079f9c-0001-0000-0000-000000000000
    common:
      box:
        log_level: 5
        memtx_memory: 268435456
    instances:
      notifications_001_01:
        cluster: notifications_001
        box:
          instance_uuid: 11079f9c-0001-0001-0000-000000000000
          listen: 10.0.3.11:4011
      notifications_001_02:
        cluster: notifications_001
        box:
          instance_uuid: 11079f9c-0001-0002-0000-000000000000
          listen: 10.0.3.12:4012
      notifications_002_01:
        cluster: notifications_002
        box:
          instance_uuid: 11079f9c-0002-0001-0000-000000000000
          listen: 10.0.3.11:4021
      notifications_002_02:
        cluster: notifications_002
        box:
          instance_uuid: 11079f9c-0002-0002-0000-000000000000
          listen: 10.0.3.12:4022

This configuration describes configuration of application notifications with 2 replicasets notifications_001 and notifications_002.

Shard notifications_001 contains 2 nodes:

• notifications_001_01 - described as master
• notifications_001_02

Shard notifications_002 contains 2 nodes:

• notifications_002_01 - described as master
• notifications_002_02

Multi-shard topology for vshard-based applications (etcd.cluster.vshard)

In most cases for multi-shard applications it is better to use module tarantool/vshard.

vshard required to be properly configured. Each instance of the cluster must contain the same view of cluster topology.

vshard application has 2 groups of instances: storages (data nodes) and routers (stateless proxy nodes).

Example of ETCD configuration for vshard-based applications (etcd.cluster.vshard)

tarantool:
  profile:
    common:
      vshard:
        bucket_count: 30000
      box:
        log_level: 5
        replication_connect_quorum: 2
    clusters:
      profile_001:
        master: profile_001_01
        replicaset_uuid: 17120f91-0001-0000-0000-000000000000
      profile_002:
        master: profile_002_01
        replicaset_uuid: 17120f91-0002-0000-0000-000000000000
    instances:
      profile_001_01:
        cluster: profile_001
        box:
          instance_uuid: 17120f91-0001-0001-0000-000000000000
          listen: 10.0.4.11:4011
      profile_001_02:
        cluster: profile_001
        box:
          instance_uuid: 17120f91-0001-0002-0000-000000000000
          listen: 10.0.4.12:4012
      profile_002_01:
        cluster: profile_002
        box:
          instance_uuid: 17120f91-0002-0001-0000-000000000000
          listen: 10.0.4.11:4021
      profile_002_02:
        cluster: profile_002
        box:
          instance_uuid: 17120f91-0002-0002-0000-000000000000
          listen: 10.0.4.12:4022
      router_001:
        router: true
        box:
          instance_uuid: 12047e12-0000-0001-0000-000000000000
          listen: 10.0.5.12:7001
      router_002:
        router: true
        box:
          instance_uuid: 12047e12-0000-0002-0000-000000000000
          listen: 10.0.5.13:7002
      router_003:
        router: true
        box:
          instance_uuid: 12047e12-0000-0003-0000-000000000000
          listen: 10.0.5.11:7003

Example of vshard-based init.lua (etcd.cluster.vshard)

The code of simultanious bootstrap is tricky, and short safe version of it listed below

local fun = require 'fun'
--- variable instance_name must be derived somehow for each tarantool instance
--- For example from name of the file. or from environment variable
require 'config' {
    mkdir = true,
    instance_name = instance_name,
    file  = '/etc/profile/conf.lua',
    master_selection_policy = 'etcd.cluster.vshard',
    on_load = function(conf, cfg)
        -- on_load is called each time right after fetching data from ETCD
        local all_cfg = conf.etcd:get_all()

        -- Construct vshard/sharding table from ETCD
        cfg.sharding = fun.iter(all_cfg.clusters)
            :map(function(shard_name, shard_info)
                return shard_info.replicaset_uuid, {
                    replicas = fun.iter(all_cfg.instances)
                        :grep(function(instance_name, instance_info)
                            return instance_info.cluster == shard_name
                        end)
                        :map(function(instance_name, instance_info)
                            return instance_info.box.instance_uuid, {
                                name   = instance_name,
                                uri    = 'guest:@'..instance_info.box.listen,
                                master = instance_name == shard_info.master,
                            }
                        end)
                        :tomap()
                }
            end)
            :tomap()
    end,
    on_after_cfg = function(conf, cfg)
        -- on_after_cfg is called once after returning from box.cfg (Tarantool is already online)
        if cfg.cluster then
            vshard.storage.cfg({
                sharding = cfg.sharding,
                bucket_count = config.get('vshard.bucket_count'),
            }, box.info.uuid)
        end
        if cfg.router then
            vshard.router.cfg({
                sharding = cfg.sharding,
                bucket_count = config.get('vshard.bucket_count'),
            })
        end
    end,
}

VShard Maintenance

By default vshard does not support master auto discovery. If you switch master in any replicaset you have to reconfigure routers as well.

With vshard topology it is strongly recommended to use package.reload. Module must be required before first require of config.

require 'package.reload'
-- ....
require 'config' {
    -- ...
}
-- ...

It is good to use switchover to maintenance sharded applications.

To get used to vshard please read getting started of it Sharding with Vshard