Promote HEAT_ENV

Promote values set in the Heat environment file to take precedence over input environment variables.

Problem Description

Historically TripleO scripts have consulted the environment for many items of configuration. This raises risks of scope leakage and the number of environment variables required often forces users to manage their environment with scripts. Consequently, there’s a push to prefer data files like the Heat environment file (HEAT_ENV) which may be set by passing -e to Heat. To allow this file to provide an unambiguous source of truth, the environment must not be allowed to override the values from this file. That is to say, precedence must be transferred.

A key distinction is whether the value of an environment variable is obtained from the environment passed to it by its parent process (either directly or through derivation). Those which are will be referred to as “input variables” and are deprecated by this spec. Those which are not will be called “local variables” and may be introduced freely. Variables containing values synthesised from multiple sources must be handled on a case-by-case basis.

Proposed Change

Since changes I5b7c8a27a9348d850d1a6e4ab79304cf13697828 and I42a9d4b85edcc99d13f7525e964baf214cdb7cbf, ENV_JSON (the contents of the file named by HEAT_ENV) is constructed in like so:

ENV_JSON=$(jq '.parameters = {
  "MysqlInnodbBufferPoolSize": 100
} + .parameters + {
  "AdminPassword": "'"${UNDERCLOUD_ADMIN_PASSWORD}"'",
  "AdminToken": "'"${UNDERCLOUD_ADMIN_TOKEN}"'",
  "CeilometerPassword": "'"${UNDERCLOUD_CEILOMETER_PASSWORD}"'",
  "GlancePassword": "'"${UNDERCLOUD_GLANCE_PASSWORD}"'",
  "HeatPassword": "'"${UNDERCLOUD_HEAT_PASSWORD}"'",
  "NovaPassword": "'"${UNDERCLOUD_NOVA_PASSWORD}"'",
  "NeutronPassword": "'"${UNDERCLOUD_NEUTRON_PASSWORD}"'",
  "NeutronPublicInterface": "'"${NeutronPublicInterface}"'",
  "undercloudImage": "'"${UNDERCLOUD_ID}"'",
  "BaremetalArch": "'"${NODE_ARCH}"'",
  "PowerSSHPrivateKey": "'"${POWER_KEY}"'",
  "NtpServer": "'"${UNDERCLOUD_NTP_SERVER}"'"
}' <<< $ENV_JSON)

This is broadly equivalent to “A + B + C”, where values from B override those from A and values from C override those from either. Currently section C contains a mix of input variables and local variables. It is proposed that current and future environment variables are allocated such that:

  • A only contains default values.
  • B is the contents of the HEAT_ENV file (from either the user or a prior run).
  • C only contains computed values (from local variables).

The following are currently in section C but are not local vars:

NeutronPublicInterface (default 'eth0')

The input variables will be ignored and the defaults moved into section A:

ENV_JSON=$(jq '.parameters = {
  "MysqlInnodbBufferPoolSize": 100,
  "NeutronPublicInterface": "eth0",
  "NtpServer": ""
} + .parameters + {
  ... elided ...
}' <<< $ENV_JSON) will be dealt with similarly. These are the variables which need to be removed and their defaults added to section A:

OVERCLOUD_NAME (default '')
NeutronPublicInterface (default 'eth0')

Only one out of all these input variables is used outside of these two scripts and consequently the rest are safe to remove.

The exception is OVERCLOUD_LIBVIRT_TYPE. This is saved by the script ‘write-tripleorc’. As it will now be preserved in HEAT_ENV, it does not need to also be preserved by write-tripleorc and can be removed from there.

So that users know they need to start setting these values through HEAT_ENV rather than input variables, it is further proposed that for an interim period each script echo a message to STDERR if deprecated input variables are set. For example:

  if [ ! -z "${!OLD_VAR}" ]; then
    echo "WARNING: ${OLD_VAR} is deprecated, please set this in the" \
         "HEAT_ENV file (${HEAT_ENV})" 1>&2

To separate user input from generated values further, it is proposed that user values be read from a new file - USER_HEAT_ENV. This will default to {under,over}cloud-user-env.json. A new commandline parameter, –user-heat-env, will be added to both scripts so that this can be changed.

  1. ENV_JSON is initialised with default values.
  2. ENV_JSON is overlaid by HEAT_ENV.
  3. ENV_JSON is overlaid by USER_HEAT_ENV.
  4. ENV_JSON is overlaid by computed values.
  5. ENV_JSON is saved to HEAT_ENV.

See for an example of how to accomplish this. In short:

ENV_JSON=$(cat ${HEAT_ENV} ${USER_HEAT_ENV} | jq -s '
  .[0] + .[1] + {"parameters":
    ({..defaults..} + .[0].parameters + {..computed..} + .[1].parameters)}')
cat > "${HEAT_ENV}" <<< ${ENV_JSON}

Choosing to move user data into a new file, compared to moving the merged data, makes USER_HEAT_ENV optional. If users wish, they can continue providing their values in HEAT_ENV. The complementary solution requires users to clean precomputed values out of HEAT_ENV, or they risk unintentionally preventing the values from being recomputed.

Loading computed values after user values sacrifices user control in favour of correctness. Considering that any devtest user must be rather technical, if a computation is incorrect they can fix or at least hack the computation themselves.


Instead of removing the input variables entirely, an interim form could be used:

ENV_JSON=$(jq '.parameters = {
  "MysqlInnodbBufferPoolSize": 100,
  "NeutronPublicInterface": "'"${NeutronPublicInterface}"'",
  "NtpServer": "'"${UNDERCLOUD_NTP_SERVER}"'"
} + .parameters + {

However, the input variables would only have an effect if the keys they affect are not present in HEAT_ENV. As HEAT_ENV is written each time devtest runs, the keys will usually be present unless the file is deleted each time (rendering it pointless). So this form is more likely to cause confusion than aid transition.

jq includes an ‘alternative operator’, //, which is intended for providing defaults:

A filter of the form a // b produces the same results as a, if a produces
results other than false and null. Otherwise, a // b produces the same
results as b.

This has not been used in the proposal for two reasons:

  1. It only works on individual keys, not whole maps.
  2. It doesn’t work in jq 1.2, still included by Ubuntu 13.04 (Saucy).

Security Impact


Other End User Impact

An announcement will be made on the mailing list when this change merges. This coupled with the warnings given if the deprecated variables are set should provide sufficient notice.

As HEAT_ENV is rewritten every time devtest executes, we can safely assume it matches the last environment used. However users who use scripts to switch their environment may be surprised. Overall the change should be a benefit to these users, as they can use two separate HEAT_ENV files (passing –heat-env to specify which to activate) instead of needing to maintain scripts to set up their environment and risking settings leaking from one to the other.

Performance Impact


Other Deployer Impact


Developer Impact





Work Items

  • Add USER_HEAT_ENV to both scripts.
  • Move variables in both scripts.
  • Add deprecated variables warning to both scripts.
  • Remove OVERCLOUD_LIBVIRT_TYPE from write-tripleorc.




The change will be tested in isolation from the rest of the script.

Documentation Impact

  • Update usage docs with env var deprecation warnings.
  • Update usage docs to recommend HEAT_ENV.


  1. - JQ manual
  2. - JQ interactive demo