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

@@ -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.

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

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);

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
+}

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"