OpenStack heat get ResourceGroup ip address and set to params - openstack-heat

Question

Create 1 master instance node and 2 minion instances from heat template.
I want to write minion_group all instances ip addresses into master instance ip.txt file.
The minion group ip addresses get from {get_attr: [minion_group, first_address] }
but this type return was not string.
So it can't use str_replace.
Does anyone have ideas?
Here is my template about resource section:
resources:
master:
type: OS::Nova::Server
depends_on: minion_group
properties:
flavor: {get_param: master_flavor}
image: {get_param: image}
key_name: {get_param: key}
networks:
- port: {get_param: network}
user_data_format: SOFTWARE_CONFIG
minion_group:
type: OS::Heat::ResourceGroup
properties:
count: 2
resource_def:
type: OS::Nova::Server
properties:
name:
list_join:
- '-'
- [{ get_param: 'OS::stack_name' }, 'minion', '%index%']
flavor: {get_param: minion_flavor}
image: {get_param: image}
key_name: {get_param: key}
networks:
- network: {get_param: network}
get_ip:
type: OS::Heat::SoftwareConfig
properties:
group: script
config:
str_replace:
template: |
#!/bin/bash
echo ${minion_group_ip} > /opt/ip.txt
params:
$minion_group_ip: {get_attr: [minion_group, first_address] }
deployment:
type: OS::Heat::SoftwareDeployment
properties:
signal_transport: HEAT_SIGNAL
config: {get_resource: get_ip}
server: {get_resource: master}