diff --git a/functions-common b/functions-common
index a97cf0dcee..f6a525354f 100644
--- a/functions-common
+++ b/functions-common
@@ -28,7 +28,6 @@
 # - ``REQUIREMENTS_DIR``
 # - ``STACK_USER``
 # - ``TRACK_DEPENDS``
-# - ``UNDO_REQUIREMENTS``
 # - ``http_proxy``, ``https_proxy``, ``no_proxy``
 #
 
diff --git a/inc/python b/inc/python
index 54e19a7886..5c9dc5c3e5 100644
--- a/inc/python
+++ b/inc/python
@@ -67,7 +67,6 @@ function pip_install_gr {
 # Wrapper for ``pip install`` to set cache and proxy environment variables
 # Uses globals ``OFFLINE``, ``PIP_VIRTUAL_ENV``,
 # ``PIP_UPGRADE``, ``TRACK_DEPENDS``, ``*_proxy``,
-# ``USE_CONSTRAINTS``
 # pip_install package [package ...]
 function pip_install {
     local xtrace=$(set +o | grep xtrace)
@@ -105,11 +104,8 @@ function pip_install {
     fi
 
     cmd_pip="$cmd_pip install"
-
-    # Handle a constraints file, if needed.
-    if [[ "$USE_CONSTRAINTS" == "True" ]]; then
-        cmd_pip="$cmd_pip -c $REQUIREMENTS_DIR/upper-constraints.txt"
-    fi
+    # Always apply constraints
+    cmd_pip="$cmd_pip -c $REQUIREMENTS_DIR/upper-constraints.txt"
 
     local pip_version=$(python -c "import pip; \
                         print(pip.__version__.strip('.')[0])")
@@ -187,13 +183,13 @@ function setup_dev_lib {
 # use this, especially *oslo* ones
 function setup_install {
     local project_dir=$1
-    setup_package_with_req_sync $project_dir
+    setup_package_with_constraints_edit $project_dir
 }
 
 # this should be used for projects which run services, like all services
 function setup_develop {
     local project_dir=$1
-    setup_package_with_req_sync $project_dir -e
+    setup_package_with_constraints_edit $project_dir -e
 }
 
 # determine if a project as specified by directory is in
@@ -209,32 +205,16 @@ function is_in_projects_txt {
 # ``pip install -e`` the package, which processes the dependencies
 # using pip before running `setup.py develop`
 #
-# Updates the dependencies in project_dir from the
-# openstack/requirements global list before installing anything.
+# Updates the constraints from REQUIREMENTS_DIR to reflect the
+# future installed state of this package. This ensures when we
+# install this package we get the from source version.
 #
-# Uses globals ``TRACK_DEPENDS``, ``REQUIREMENTS_DIR``, ``UNDO_REQUIREMENTS``
+# Uses globals ``REQUIREMENTS_DIR``
 # setup_develop directory
-function setup_package_with_req_sync {
+function setup_package_with_constraints_edit {
     local project_dir=$1
     local flags=$2
 
-    # Don't update repo if local changes exist
-    # Don't use buggy "git diff --quiet"
-    # ``errexit`` requires us to trap the exit code when the repo is changed
-    local update_requirements=$(cd $project_dir && git diff --exit-code >/dev/null || echo "changed")
-
-    if [[ $update_requirements != "changed" && "$USE_CONSTRAINTS" == "False" ]]; then
-        if is_in_projects_txt $project_dir; then
-            (cd $REQUIREMENTS_DIR; \
-                ./.venv/bin/python update.py $project_dir)
-        else
-            # soft update projects not found in requirements project.txt
-            echo "$project_dir not a constrained repository, soft enforcing requirements"
-            (cd $REQUIREMENTS_DIR; \
-                ./.venv/bin/python update.py -s $project_dir)
-        fi
-    fi
-
     if [ -n "$REQUIREMENTS_DIR" ]; then
         # Constrain this package to this project directory from here on out.
         local name=$(awk '/^name.*=/ {print $3}' $project_dir/setup.cfg)
@@ -245,19 +225,6 @@ function setup_package_with_req_sync {
 
     setup_package $project_dir $flags
 
-    # We've just gone and possibly modified the user's source tree in an
-    # automated way, which is considered bad form if it's a development
-    # tree because we've screwed up their next git checkin. So undo it.
-    #
-    # However... there are some circumstances, like running in the gate
-    # where we really really want the overridden version to stick. So provide
-    # a variable that tells us whether or not we should UNDO the requirements
-    # changes (this will be set to False in the OpenStack ci gate)
-    if [ $UNDO_REQUIREMENTS = "True" ]; then
-        if [[ $update_requirements != "changed" ]]; then
-            (cd $project_dir && git reset --hard)
-        fi
-    fi
 }
 
 # ``pip install -e`` the package, which processes the dependencies
diff --git a/lib/infra b/lib/infra
index eb8000e8d3..89397de792 100644
--- a/lib/infra
+++ b/lib/infra
@@ -22,7 +22,6 @@ set +o xtrace
 # Defaults
 # --------
 GITDIR["pbr"]=$DEST/pbr
-REQUIREMENTS_DIR=$DEST/requirements
 
 # Entry Points
 # ------------
diff --git a/stack.sh b/stack.sh
index e9247295e7..341df7fc92 100755
--- a/stack.sh
+++ b/stack.sh
@@ -688,9 +688,6 @@ save_stackenv $LINENO
 echo_summary "Installing package prerequisites"
 source $TOP_DIR/tools/install_prereqs.sh
 
-# Normalise USE_CONSTRAINTS
-USE_CONSTRAINTS=$(trueorfalse False USE_CONSTRAINTS)
-
 # Configure an appropriate Python environment
 if [[ "$OFFLINE" != "True" ]]; then
     PYPI_ALTERNATIVE_URL=${PYPI_ALTERNATIVE_URL:-""} $TOP_DIR/tools/install_pip.sh
diff --git a/stackrc b/stackrc
index f4245a40cf..156cb1f85a 100644
--- a/stackrc
+++ b/stackrc
@@ -152,13 +152,6 @@ DATABASE_QUERY_LOGGING=$(trueorfalse False DATABASE_QUERY_LOGGING)
 # Zero disables timeouts
 GIT_TIMEOUT=${GIT_TIMEOUT:-0}
 
-# Constraints mode
-# - False (default) : update git projects dependencies from global-requirements.
-#
-# - True : use upper-constraints.txt to constrain versions of packages intalled
-#          and do not edit projects at all.
-USE_CONSTRAINTS=$(trueorfalse False USE_CONSTRAINTS)
-
 # Repositories
 # ------------
 
@@ -166,6 +159,9 @@ USE_CONSTRAINTS=$(trueorfalse False USE_CONSTRAINTS)
 # Another option is https://git.openstack.org
 GIT_BASE=${GIT_BASE:-git://git.openstack.org}
 
+# The location of REQUIREMENTS once cloned
+REQUIREMENTS_DIR=$DEST/requirements
+
 # Which libraries should we install from git instead of using released
 # versions on pypi?
 #
@@ -630,9 +626,6 @@ USE_SCREEN=${SCREEN_DEV:-$USE_SCREEN}
 # Set default screen name
 SCREEN_NAME=${SCREEN_NAME:-stack}
 
-# Undo requirements changes by global requirements
-UNDO_REQUIREMENTS=${UNDO_REQUIREMENTS:-True}
-
 # Allow the use of an alternate protocol (such as https) for service endpoints
 SERVICE_PROTOCOL=${SERVICE_PROTOCOL:-http}
 
diff --git a/tools/install_pip.sh b/tools/install_pip.sh
index 0f7c962b2b..7b42c8c485 100755
--- a/tools/install_pip.sh
+++ b/tools/install_pip.sh
@@ -20,7 +20,7 @@ TOP_DIR=`cd $TOOLS_DIR/..; pwd`
 cd $TOP_DIR
 
 # Import common functions
-source $TOP_DIR/functions
+source $TOP_DIR/stackrc
 
 FILES=$TOP_DIR/files