FIX: Flaky SRV-backed model seeding. (#708)

* Seeding the SRV-backed model should happen inside an initializer.
* Keep the model up to date when the hidden setting changes.
* Use the correct Mixtral model name and fix previous data migration.
* URL validation should trigger only when we attempt to update it.

app/models/llm_model.rb

@@ -7,24 +7,36 @@ class LlmModel < ActiveRecord::Base
 
   belongs_to :user
 
-  validates :url, exclusion: { in: [RESERVED_VLLM_SRV_URL] }
+  validates :url, exclusion: { in: [RESERVED_VLLM_SRV_URL] }, if: :url_changed?
 
-  def self.enable_or_disable_srv_llm!
+  def self.seed_srv_backed_model
+    srv = SiteSetting.ai_vllm_endpoint_srv
     srv_model = find_by(url: RESERVED_VLLM_SRV_URL)
-    if SiteSetting.ai_vllm_endpoint_srv.present? && srv_model.blank?
-      record =
-        new(
-          display_name: "vLLM SRV LLM",
-          name: "mistralai/Mixtral",
-          provider: "vllm",
-          tokenizer: "DiscourseAi::Tokenizer::MixtralTokenizer",
-          url: RESERVED_VLLM_SRV_URL,
-          max_prompt_tokens: 8000,
-        )
 
-      record.save(validate: false) # Ignore reserved URL validation
-    elsif srv_model.present?
-      srv_model.destroy!
+    if srv.present?
+      if srv_model.present?
+        current_key = SiteSetting.ai_vllm_api_key
+        srv_model.update!(api_key: current_key) if current_key != srv_model.api_key
+      else
+        record =
+          new(
+            display_name: "vLLM SRV LLM",
+            name: "mistralai/Mixtral-8x7B-Instruct-v0.1",
+            provider: "vllm",
+            tokenizer: "DiscourseAi::Tokenizer::MixtralTokenizer",
+            url: RESERVED_VLLM_SRV_URL,
+            max_prompt_tokens: 8000,
+            api_key: SiteSetting.ai_vllm_api_key,
+          )
+
+        record.save(validate: false) # Ignore reserved URL validation
+      end
+    else
+      # Clean up companion users
+      srv_model&.enabled_chat_bot = false
+      srv_model&.toggle_companion_user
+
+      srv_model&.destroy!
     end
   end
 

db/fixtures/602_srv_backed_llm_model.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+begin
+  LlmModel.seed_srv_backed_model
+rescue PG::UndefinedColumn => e
+  # If this code runs before migrations, an attribute might be missing.
+  Rails.logger.warn("Failed to seed SRV-Backed LLM: #{e.meesage}")
+end

db/post_migrate/20240708193243_fix_vllm_model_name.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+class FixVllmModelName < ActiveRecord::Migration[7.1]
+  def up
+    vllm_mixtral_model_id = DB.query_single(<<~SQL).first
+      SELECT id FROM llm_models WHERE name = 'mistralai/Mixtral'
+    SQL
+
+    DB.exec(<<~SQL, target_id: vllm_mixtral_model_id) if vllm_mixtral_model_id
+      UPDATE llm_models
+      SET name = 'mistralai/Mixtral-8x7B-Instruct-v0.1'
+      WHERE id = :target_id
+    SQL
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end

plugin.rb

@@ -47,8 +47,6 @@ after_initialize do
 
   add_admin_route("discourse_ai.title", "discourse-ai", { use_new_show_route: true })
 
-  LlmModel.enable_or_disable_srv_llm!
-
   [
     DiscourseAi::Embeddings::EntryPoint.new,
     DiscourseAi::Nsfw::EntryPoint.new,
@@ -82,4 +80,8 @@ after_initialize do
       nil
     end
   end
+
+  on(:site_setting_changed) do |name, _old_value, _new_value|
+    LlmModel.seed_srv_backed_model if name == :ai_vllm_endpoint_srv || name == :ai_vllm_api_key
+  end
 end

spec/models/llm_model_spec.rb

@@ -0,0 +1,64 @@
+# frozen_string_literal: true
+
+RSpec.describe LlmModel do
+  describe ".seed_srv_backed_model" do
+    before do
+      SiteSetting.ai_vllm_endpoint_srv = "srv.llm.service."
+      SiteSetting.ai_vllm_api_key = "123"
+    end
+
+    context "when the model doesn't exist yet" do
+      it "creates it" do
+        described_class.seed_srv_backed_model
+
+        llm_model = described_class.find_by(url: described_class::RESERVED_VLLM_SRV_URL)
+
+        expect(llm_model).to be_present
+        expect(llm_model.name).to eq("mistralai/Mixtral-8x7B-Instruct-v0.1")
+        expect(llm_model.api_key).to eq(SiteSetting.ai_vllm_api_key)
+      end
+    end
+
+    context "when the model already exists" do
+      before { described_class.seed_srv_backed_model }
+
+      context "when the API key setting changes" do
+        it "updates it" do
+          new_key = "456"
+          SiteSetting.ai_vllm_api_key = new_key
+
+          described_class.seed_srv_backed_model
+
+          llm_model = described_class.find_by(url: described_class::RESERVED_VLLM_SRV_URL)
+
+          expect(llm_model.api_key).to eq(new_key)
+        end
+      end
+
+      context "when the SRV is no longer defined" do
+        it "deletes the LlmModel" do
+          llm_model = described_class.find_by(url: described_class::RESERVED_VLLM_SRV_URL)
+          expect(llm_model).to be_present
+
+          SiteSetting.ai_vllm_endpoint_srv = "" # Triggers seed code
+
+          expect { llm_model.reload }.to raise_exception(ActiveRecord::RecordNotFound)
+        end
+
+        it "disabled the bot user" do
+          SiteSetting.ai_bot_enabled = true
+          llm_model = described_class.find_by(url: described_class::RESERVED_VLLM_SRV_URL)
+          llm_model.update!(enabled_chat_bot: true)
+          llm_model.toggle_companion_user
+          user = llm_model.user
+
+          expect(user).to be_present
+
+          SiteSetting.ai_vllm_endpoint_srv = "" # Triggers seed code
+
+          expect { user.reload }.to raise_exception(ActiveRecord::RecordNotFound)
+        end
+      end
+    end
+  end
+end