Introduce predictable environment slugs

If an environment slug is predictable given only the environment
name, we can use the environment slug earlier in the CI variable
evaluation process as we don't have to wait for the environment
record itself to be persisted.

app/models/environment.rb

@@ -4,11 +4,6 @@ class Environment < ApplicationRecord
   include Gitlab::Utils::StrongMemoize
   include ReactiveCaching
 
-  # Used to generate random suffixes for the slug
-  LETTERS = ('a'..'z').freeze
-  NUMBERS = ('0'..'9').freeze
-  SUFFIX_CHARS = LETTERS.to_a + NUMBERS.to_a
-
   belongs_to :project, required: true
 
   has_many :deployments, -> { success }, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
@@ -203,40 +198,6 @@ class Environment < ApplicationRecord
     super.presence || generate_slug
   end
 
-  # An environment name is not necessarily suitable for use in URLs, DNS
-  # or other third-party contexts, so provide a slugified version. A slug has
-  # the following properties:
-  #   * contains only lowercase letters (a-z), numbers (0-9), and '-'
-  #   * begins with a letter
-  #   * has a maximum length of 24 bytes (OpenShift limitation)
-  #   * cannot end with `-`
-  def generate_slug
-    # Lowercase letters and numbers only
-    slugified = +name.to_s.downcase.gsub(/[^a-z0-9]/, '-')
-
-    # Must start with a letter
-    slugified = 'env-' + slugified unless LETTERS.cover?(slugified[0])
-
-    # Repeated dashes are invalid (OpenShift limitation)
-    slugified.gsub!(/\-+/, '-')
-
-    # Maximum length: 24 characters (OpenShift limitation)
-    slugified = slugified[0..23]
-
-    # Cannot end with a dash (Kubernetes label limitation)
-    slugified.chop! if slugified.end_with?('-')
-
-    # Add a random suffix, shortening the current string if necessary, if it
-    # has been slugified. This ensures uniqueness.
-    if slugified != name
-      slugified = slugified[0..16]
-      slugified << '-' unless slugified.end_with?('-')
-      slugified << random_suffix
-    end
-
-    self.slug = slugified
-  end
-
   def external_url_for(path, commit_sha)
     return unless self.external_url
 
@@ -274,11 +235,7 @@ class Environment < ApplicationRecord
 
   private
 
-  # Slugifying a name may remove the uniqueness guarantee afforded by it being
-  # based on name (which must be unique). To compensate, we add a random
-  # 6-byte suffix in those circumstances. This is not *guaranteed* uniqueness,
-  # but the chance of collisions is vanishingly small
-  def random_suffix
-    (0..5).map { SUFFIX_CHARS.sample }.join
+  def generate_slug
+    self.slug = Gitlab::Slug::Environment.new(name).generate
   end
 end

changelogs/unreleased/64295-predictable-environment-slugs.yml

+---
+title: Use predictable environment slugs
+merge_request: 30551
+author:
+type: added

lib/gitlab/slug/environment.rb

+# frozen_string_literal: true
+
+# An environment name is not necessarily suitable for use in URLs, DNS
+# or other third-party contexts, so provide a slugified version. A slug has
+# the following properties:
+#   * contains only lowercase letters (a-z), numbers (0-9), and '-'
+#   * begins with a letter
+#   * has a maximum length of 24 bytes (OpenShift limitation)
+#   * cannot end with `-`
+module Gitlab
+  module Slug
+    class Environment
+      attr_reader :name
+
+      def initialize(name)
+        @name = name
+      end
+
+      def generate
+        # Lowercase letters and numbers only
+        slugified = name.to_s.downcase.gsub(/[^a-z0-9]/, '-')
+
+        # Must start with a letter
+        slugified = 'env-' + slugified unless slugified.match?(/^[a-z]/)
+
+        # Repeated dashes are invalid (OpenShift limitation)
+        slugified.squeeze!('-')
+
+        slugified =
+          if slugified.size > 24 || slugified != name
+            # Maximum length: 24 characters (OpenShift limitation)
+            shorten_and_add_suffix(slugified)
+          else
+            # Cannot end with a dash (Kubernetes label limitation)
+            slugified.chomp('-')
+          end
+
+        slugified
+      end
+
+      private
+
+      def shorten_and_add_suffix(slug)
+        slug = slug[0..16]
+        slug << '-' unless slug.ends_with?('-')
+        slug << suffix
+      end
+
+      # Slugifying a name may remove the uniqueness guarantee afforded by it being
+      # based on name (which must be unique). To compensate, we add a predictable
+      # 6-byte suffix in those circumstances. This is not *guaranteed* uniqueness,
+      # but the chance of collisions is vanishingly small
+      def suffix
+        Digest::SHA2.hexdigest(name.to_s).to_i(16).to_s(36).last(6)
+      end
+    end
+  end
+end

spec/lib/gitlab/slug/environment_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::Slug::Environment do
+  describe '#generate' do
+    {
+      "staging-12345678901234567" => "staging-123456789-q517sa",
+      "9-staging-123456789012345" => "env-9-staging-123-q517sa",
+      "staging-1234567890123456"  => "staging-1234567890123456",
+      "staging-1234567890123456-" => "staging-123456789-q517sa",
+      "production"                => "production",
+      "PRODUCTION"                => "production-q517sa",
+      "review/1-foo"              => "review-1-foo-q517sa",
+      "1-foo"                     => "env-1-foo-q517sa",
+      "1/foo"                     => "env-1-foo-q517sa",
+      "foo-"                      => "foo",
+      "foo--bar"                  => "foo-bar-q517sa",
+      "foo**bar"                  => "foo-bar-q517sa",
+      "*-foo"                     => "env-foo-q517sa",
+      "staging-12345678-"         => "staging-12345678",
+      "staging-12345678-01234567" => "staging-12345678-q517sa",
+      ""                          => "env-q517sa",
+      nil                         => "env-q517sa"
+    }.each do |name, matcher|
+      before do
+        # ('a' * 64).to_i(16).to_s(36).last(6) gives 'q517sa'
+        allow(Digest::SHA2).to receive(:hexdigest).with(name).and_return('a' * 64)
+      end
+
+      it "returns a slug matching #{matcher}, given #{name}" do
+        slug = described_class.new(name).generate
+
+        expect(slug).to match(/\A#{matcher}\z/)
+      end
+    end
+  end
+end

spec/models/environment_spec.rb

@@ -762,32 +762,6 @@ describe Environment, :use_clean_rails_memory_store_caching do
     end
   end
 
-  describe '#generate_slug' do
-    SUFFIX = "-[a-z0-9]{6}".freeze
-    {
-      "staging-12345678901234567" => "staging-123456789" + SUFFIX,
-      "9-staging-123456789012345" => "env-9-staging-123" + SUFFIX,
-      "staging-1234567890123456"  => "staging-1234567890123456",
-      "production"                => "production",
-      "PRODUCTION"                => "production" + SUFFIX,
-      "review/1-foo"              => "review-1-foo" + SUFFIX,
-      "1-foo"                     => "env-1-foo" + SUFFIX,
-      "1/foo"                     => "env-1-foo" + SUFFIX,
-      "foo-"                      => "foo" + SUFFIX,
-      "foo--bar"                  => "foo-bar" + SUFFIX,
-      "foo**bar"                  => "foo-bar" + SUFFIX,
-      "*-foo"                     => "env-foo" + SUFFIX,
-      "staging-12345678-"         => "staging-12345678" + SUFFIX,
-      "staging-12345678-01234567" => "staging-12345678" + SUFFIX
-    }.each do |name, matcher|
-      it "returns a slug matching #{matcher}, given #{name}" do
-        slug = described_class.new(name: name).generate_slug
-
-        expect(slug).to match(/\A#{matcher}\z/)
-      end
-    end
-  end
-
   describe '#ref_path' do
     subject(:environment) do
       create(:environment, name: 'staging / review-1')