From 07e7988cdf1e0422ad5314cbc1aad2783c2bef79 Mon Sep 17 00:00:00 2001
From: Jose Diaz-Gonzalez <email@josediazgonzalez.com>
Date: Wed, 30 Dec 2020 05:48:29 -0500
Subject: [PATCH] feat: add sigil templating to CHECKS files

This enables general templating capabilities, in addition to environment variable access.

Closes #3974.
---
 docs/deployment/zero-downtime-deploys.md    | 32 +++++++++++++++++++++
 plugins/scheduler-docker-local/check-deploy |  9 ++++++
 tests/apps/nodejs-express/web.js            |  4 +++
 tests/unit/checks.bats                      | 13 +++++++++
 tests/unit/test_helper.bash                 | 14 +++++++++
 5 files changed, 72 insertions(+)

diff --git a/docs/deployment/zero-downtime-deploys.md b/docs/deployment/zero-downtime-deploys.md
index 88e2b296a..343c4eb9f 100644
--- a/docs/deployment/zero-downtime-deploys.md
+++ b/docs/deployment/zero-downtime-deploys.md
@@ -157,6 +157,38 @@ https://static.dokku.me/logo.png
 
 While a full URL may be used in order to invoke checks, if you are using relative URLs, the port *must* be omitted.
 
+> Changed as of 0.22.5
+
+Please note that dollar sign bracket characters (`{` and `}`) must be escaped when used within a `CHECKS` file. Escaping follows golang template rules. The proper way to do this is via one of the following methods:
+
+```
+# escaping the `{` character
+# using double-quotes
+{{"{"}}
+
+# using raw string constants
+{{`{`}}
+
+# escaping the `}` character
+# using double-quotes
+{{"}"}}
+
+# using raw string constants
+{{`}`}}
+```
+
+### Templating Checks Files
+
+> New as of 0.22.5
+
+An app's `CHECKS` file is sent through a single pass of the [`sigil`](https://github.com/gliderlabs/sigil/) templating tool. This enables usage of Golang templating within application `CHECKS` files. In addition to general templating access, access to app environment variables is also allowed via the `var` function:
+
+```
+{{ var "SOME_ENV_VAR" }}
+```
+
+This may be useful if certain zero-downtime checks require access to an app-specific value, such as a domain name.
+
 ### Check settings
 
 The default behavior is to wait for `5` seconds before running the checks, to timeout the checks after `30` seconds, and to attempt the checks `5` times. If the checks fail `5` times, the deployment is considered failed and the old container will continue serving traffic.
diff --git a/plugins/scheduler-docker-local/check-deploy b/plugins/scheduler-docker-local/check-deploy
index e88995891..de7f49a9d 100755
--- a/plugins/scheduler-docker-local/check-deploy
+++ b/plugins/scheduler-docker-local/check-deploy
@@ -115,6 +115,15 @@ trigger-scheduler-docker-local-check-deploy() {
     dokku_log_verbose "Default container check successful!" && exit 0
   fi
 
+  local NEW_CHECKS_FILENAME=${CHECK_DEPLOY_TMP_WORK_DIR}/$(mktemp dokku-${FUNCNAME[0]}-CHECKS.XXXX)
+  template_checks() {
+    eval "$(config_export app "$APP" --merged)"
+    sigil -f "$CHECKS_FILENAME" | cat -s >"$NEW_CHECKS_FILENAME"
+  }
+
+  template_checks
+  CHECKS_FILENAME="$NEW_CHECKS_FILENAME"
+
   # Reads name/value pairs, sets the WAIT and TIMEOUT variables
   exec <"$CHECKS_FILENAME"
   local line
diff --git a/tests/apps/nodejs-express/web.js b/tests/apps/nodejs-express/web.js
index d1d386c60..e08a9c530 100644
--- a/tests/apps/nodejs-express/web.js
+++ b/tests/apps/nodejs-express/web.js
@@ -6,6 +6,10 @@ app.get('/', function(request, response) {
   response.send('nodejs/express');
 });
 
+app.get('/healthcheck', function(request, response) {
+  response.send(process.env.HEALTHCHECK_ENDPOINT);
+});
+
 var port = process.env.PORT || 5000;
 app.listen(port, function() {
   console.log("Listening on " + port);
diff --git a/tests/unit/checks.bats b/tests/unit/checks.bats
index d0ae98d40..e337dad56 100644
--- a/tests/unit/checks.bats
+++ b/tests/unit/checks.bats
@@ -249,3 +249,16 @@ teardown() {
   echo "status: $status"
   assert_success
 }
+
+@test "(checks) checks:templated" {
+  run /bin/bash -c "dokku config:set $TEST_APP HEALTHCHECK_ENDPOINT=/healthcheck"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run deploy_app nodejs-express dokku@dokku.me:$TEST_APP template_checks_file
+  echo "output: $output"
+  echo "status: $status"
+  assert_output_contains "/healthcheck" 2
+  assert_success
+}
diff --git a/tests/unit/test_helper.bash b/tests/unit/test_helper.bash
index 379bb184f..cebb96fce 100644
--- a/tests/unit/test_helper.bash
+++ b/tests/unit/test_helper.bash
@@ -484,6 +484,20 @@ some lame nginx config
 EOF
 }
 
+template_checks_file() {
+  local APP="$1"
+  local APP_REPO_DIR="$2"
+  [[ -z "$APP" ]] && local APP="$TEST_APP"
+  echo "injecting templated CHECKS file -> $APP_REPO_DIR/CHECKS"
+  cat <<EOF >"$APP_REPO_DIR/CHECKS"
+WAIT=2 # wait 2 seconds
+TIMEOUT=5 # set timeout to 5 seconds
+ATTEMPTS=2 # try 2 times
+
+{{ var "HEALTHCHECK_ENDPOINT" }} {{ var "HEALTHCHECK_ENDPOINT" }}
+EOF
+}
+
 add_release_command() {
   local APP="$1"
   local APP_REPO_DIR="$2"