Seagull

Service for working with configuration and service-discovery via etcd or consul. Can be useful in microservices.

Configuration

Static

For configuration use sys.config:

{seagull, 
    [
        {backend, {Backend, BackendUrl}}
    ]
}

Where:
Backend is an module with implementation of sc_backend. BackendUrl is url to reach the service.
Example:

{seagull, 
        [
            {backend, {sc_backend_consul, "http://127.0.0.1:8500"}}
        ]
    }

Dynamic

In case you don't know consul url on compilation time you do not need to specify seagull configuration in sys.config. Just when you obtain you module, url and other params call seagull:add_backend/2/3. Third argument is a proplist with all your options (listed below).
Example:

seagull:add_backend(sc_backend_consul, "http://mydynamicconsul:8500", [{cache, #{enable => true, update_time => 15000}}]).

Caching kv

You can cache kv storage in ets by adding {cache, [{enable, true}]} to sys.config. By default cache is false. Also you should update interval for cache values to be synchronized with backend by adding #{update_time => TimeMS} to cache section. Default update interval is 5 sec. If you don't need to update values, set #{update_time => undefined} to disable cache values updates. Full Example:

{seagull, 
        [
            {backend, {sc_backend_consul, "http://127.0.0.1:8500"}},
            {cache, #{enable => true, update_time => 15000}}
        ]
    }

Service auto registration

To make registration of your service on application start - add seagull to your applications and add this option to seagull conf in sys.config:

{seagull, 
        [
            ...
            {autoregister, #{service => Service, address => Address, port => Port}},
            ...
        ]
    }

On update callbacks (Not implemented)

If you enabled cache update - you can add callback function, which will be called, when value is updated.
Remember, that callbacks are synchronous and are called from main conf sycle, so do not do any long operations in them.
Example:

ResetAllPassFun = fun(NewPass) -> database_man ! {reset_pass, NewPass} end, 
seagull:add_callback(<<"user_pass">>, ResetAllPassFun).

Callback can be removed with remove_callback:/1 function.

Usage

Unified api

After configuring backend you can use unified api:

1> seagull:get_services().
#{<<"consul">> => [],<<"postgres">> => [],<<"redis">> => []}

Consul special api

You can use consul special api with consul backend:

1> seagull:dns_request("redis").
[{1,1,6379,"tihon_home.node.dc1.consul"},
{1,1,6379,"tihon_work.su.node.dc1.consul"}]
2> seagull:get_service_near("redis").
{ok, #{<<"Address">> => <<"192.168.1.204">>,
        <<"CreateIndex">> => 313,
        <<"ModifyIndex">> => 313,
        <<"Node">> => <<"tihon_work.su">>,
        <<"ServiceAddress">> => <<>>,
        <<"ServiceEnableTagOverride">> => false,
        <<"ServiceID">> => <<"tihon_work.su:redis:6379">>,
        <<"ServiceName">> => <<"redis">>,
        <<"ServicePort">> => 6379,
        <<"ServiceTags">> => [],
        <<"TaggedAddresses">> => #{<<"wan">> => <<"192.168.1.204">>}}, 
        [#{<<"Address">> => <<"192.168.1.105">>,
            <<"CreateIndex">> => 231,
            <<"ModifyIndex">> => 231,
            <<"Node">> => <<"tihon_home">>,
            <<"ServiceAddress">> => <<>>,
            <<"ServiceEnableTagOverride">> => false,
            <<"ServiceID">> => <<"tihon_home:redis:6379">>,
            <<"ServiceName">> => <<"redis">>,
            <<"ServicePort">> => 6379,
            <<"ServiceTags">> => [],
            <<"TaggedAddresses">> => #{<<"lan">> => <<"192.168.1.105">>,
                <<"wan">> => <<"192.168.1.105">>}}]

Testing

To run tests of backends you will need this backends running and accessible. sc_backend_consul tries to find consul on http://127.0.0.1:8500, and sc_backend_etcd tries to find etcd on http://127.0.0.1:2379.
You can use install-deps.sh script for getting executables of theese two deps downloaded to $HOME/consul and $HOME/etcd.