telegraf: External Environment Variables are not set when running Telegraf

Relevant telegraf.conf:

[global_tags]
  env = "ENVIRONMENT"
[agent]
  interval = "60s"
  hostname = "telegraf-snmp-compute-leafs"
  omit_hostname = false
[[outputs.wavefront]]
  host = "$WF_PROXY"
  port = $WF_PORT1
  metric_separator = "."
  convert_paths = true
  use_regex = false

[[inputs.snmp]]
  agents = [AGENTS]
  version = 3
  auth_password = "$TELEGRAF_SNMP_TOKEN"
  auth_protocol = "MD5"
  priv_password = "$TELEGRAF_SNMP_TOKEN"
  priv_protocol = "AES"
  sec_name = "$SNMP_SECURITY_USER"
  sec_level = "authPriv"
  max_repetitions = 10
  timeout = "10s"
  retries = 1
  name_prefix = "dev."

  [[inputs.snmp.field]]
    name = "hostname"
    oid = ".1.3.6.1.2.1.1.5.0"
    is_tag = true

  [[inputs.snmp.field]]
    name = "cseSysCPUutilization"
    oid = ".1.3.6.1.4.1.9.9.305.1.1.1.0"
  [[inputs.snmp.field]]
    name = "cseSysUpTime"
    oid = ".1.3.6.1.4.1.9.9.305.1.1.10.0"
  [[inputs.snmp.field]]
    name = "cseSysMemoryUtilization"
    oid = ".1.3.6.1.4.1.9.9.305.1.1.2.0"

  [[inputs.snmp.table]]
    name = "interfaceStats"
    inherit_tags = ["hostname"]
    [[inputs.snmp.table.field]]
      name = "ifAlias"
      oid = ".1.3.6.1.2.1.31.1.1.1.18"
      is_tag = true
    [[inputs.snmp.table.field]]
      name = "ifName"
      oid = ".1.3.6.1.2.1.31.1.1.1.1"
      is_tag = true
    [[inputs.snmp.table.field]]
	    name = "ifType"
  	  oid = ".1.3.6.1.2.1.2.2.1.3"
    [[inputs.snmp.table.field]]
      name = "ifInNUcastPkts"
      oid = "1.3.6.1.2.1.2.2.1.12"
    [[inputs.snmp.table.field]]
      name = "ifInDiscards"
      oid = "1.3.6.1.2.1.2.2.1.13"
    [[inputs.snmp.table.field]]
      name = "ifInErrors"
      oid = "1.3.6.1.2.1.2.2.1.14"
    [[inputs.snmp.table.field]]
      name = "ifOutUcastPkts"
      oid = "1.3.6.1.2.1.2.2.1.14"
    [[inputs.snmp.table.field]]
      name = "ifOutNUcastPkts"
      oid = "1.3.6.1.2.1.2.2.1.18"
    [[inputs.snmp.table.field]]
      name = "ifOutDiscards"
      oid = "1.3.6.1.2.1.2.2.1.19"
    [[inputs.snmp.table.field]]
      name = "ifOutErrors"
      oid = "1.3.6.1.2.1.2.2.1.20"
    [[inputs.snmp.table.field]]
      name = "ifMtu"
      oid = "1.3.6.1.2.1.2.2.1.4"

System info:

DOCKER CONTAINER RUNNING telegraf:1.10-alpine

Steps to reproduce:

1. Build Docker Container and set appropriate Environment Variables. Afterwards the config file in the container does not have the appropriate values.
2. When creating env variable that is not a string, get a Error running agent: Error parsing /etc/telegraf/telegraf.conf, toml: line 9: parse error
3. Have tried the variables with “${SNMP_SECURITY_USER}” and with just “$SNMP_SECURITY_USER” and neither seem to work. Currently it works when I run the config with a sed command, but would like to pass in the variables directly instead.

Expected behavior:

The environment variables that are set in the container are populated in the config file when telegraf starts.

Actual behavior:

Getting either a parse error or the environment variable is just showing up with the variable name instead of the value.

Additional info:

Have tried the Telegraf Alpine versions 9, 10 and 10.5 and still not working.