Fix no httpd service in cartridge

CHANGELOG.md

@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 ### Fixed
 - cpu metrics hot reload [#228](https://github.com/tarantool/metrics/issues/228)
+- cartridge metrics role fails to start without http [#225](https://github.com/tarantool/metrics/issues/225)
 
 ## [0.8.0] - 2021-04-13
 ### Added

cartridge/roles/metrics.lua

@@ -84,6 +84,9 @@ local current_paths = {}
 
 local function apply_routes(export)
     local httpd = cartridge.service_get('httpd')
+    if httpd == nil then
+        return
+    end
     for _, exporter in ipairs(export) do
         local path, format = remove_side_slashes(exporter.path), exporter.format
         if current_paths[path] ~= format then

test/integration/cartridge_nohttp_test.lua

@@ -0,0 +1,55 @@
+local fio = require('fio')
+local t = require('luatest')
+local g = t.group('cartridge-without-http')
+
+local helpers = require('test.helper')
+
+local function set_export(cluster, export)
+    local server = cluster.main_server
+    return server.net_box:eval([[
+        local cartridge = require('cartridge')
+        local metrics = cartridge.service_get('metrics')
+        local _, err = pcall(
+            metrics.set_export, ...
+        )
+        return err
+    ]], {export})
+end
+
+
+g.test_http_disabled = function()
+    t.skip_if(type(helpers) ~= 'table', 'Skip cartridge test')
+    local cluster = helpers.Cluster:new({
+        datadir = fio.tempdir(),
+        server_command = helpers.entrypoint('srv_basic'),
+        replicasets = {
+            {
+                uuid = helpers.uuid('a'),
+                roles = {},
+                servers = {
+                    {instance_uuid = helpers.uuid('a', 1), alias = 'main'},
+                },
+            },
+        },
+    })
+    cluster:start()
+
+    local server = cluster.main_server
+
+    server.net_box:eval([[
+        local cartridge = require('cartridge')
+        _G.old_service = cartridge.service_get('httpd')
+        cartridge.service_set('httpd', nil)
+    ]])
+
+    local ret = set_export(cluster, {
+        {
+            path = '/metrics',
+            format = 'json',
+        },
+    })
+    t.assert_not(ret)
+
+    cluster:stop()
+    fio.rmtree(cluster.datadir)
+end