Maxmind provides free and pay-for memory mapped ip-lookup databases. The free city-level database is about 22 mB, and can be found on the geolite page.

Compile

Ensure you have libfastjson installed, check your package manager or install from source.
Ensure you have libmaxminddb installed, check your package manager.
configure

export PKG_CONFIG_PATH=/lib64/pkgconfig/
yum install -y libestr liblogging libmaxminddb-devel
yum install -y autoconf automake flex bison json-c-devel libuuid-devel libgcrypt-devel zlib-devel openssl-devel libcurl-devel gnutls-devel
cd ../rsyslog
./autogen.sh --enable-mmdblookup --enable-mmjsonparse --***
make
make install

Usage

Configuration

module( load="imfile" )
module( load="mmdblookup" )
module( load="mmjsonparse" )

input (
	type="imfile"
	File="/tmp/access.log"
	addMetadata="off"
	Severity="info"
	Facility="user"
	tag="test"
	ruleset="test"
)

template ( type="string" string="{\"@timestamp\":\"%timereported:::date-rfc3339%\",\"host\":\"%hostname%\",\"geoip2\":%$!iplocation%,%msg:7:$%" name="clientlog" )
ruleset  ( name="test" ) {
	action ( type="mmjsonparse" )
	if ( $parsesuccess == "OK" ) then {
		action( type="mmdblookup" mmdbfile="/etc/rsyslog.d/GeoLite2-City.mmdb" fields=["!continent!code","!location"] key="!clientip" )
		action( type="omfwd" Target="10.211.55.3" port="514" Protocol="tcp" template="clientlog" )
		stop
	}
}

Testing

cat /root/a
@cee:{"clientip":"202.106.0.2","os_ver":"ios8","weibo_ver":"5.4.0","uid":1234567890,"rtt":0.123456,"error_code":-10005,"error_msg":"你以为我会告诉你么"}
cat /root/a > /tmp/access

get the result from logstash-input:

{
       "message" => "{\"@timestamp\":\"2016-07-23T10:35:21.572373+08:00\",\"host\":\"localhost\",\"geoip2\":{ \"continent\": { \"code\": \"AS\" }, \"location\": { \"accuracy_radius\": 50, \"latitude\": 34.772500, \"longitude\": 113.726600 } },\"clientip\":\"202.106.0.2\",\"os_ver\":\"ios8\",\"weibo_ver\":\"5.4.0\",\"uid\":1234567890,\"rtt\":0.123456,\"error_code\":-10005,\"error_msg\":\"你以为我会告诉你么\"}",
      "@version" => "1",
    "@timestamp" => "2016-07-23T02:35:21.586Z",
          "host" => "10.211.55.3",
          "port" => 58199
}