Server fails to start if basePath is set to an empty string

[tehmoon]

Kibana version: 7.5.0

Elasticsearch version: 7.5.0

Server OS version: ubuntu 16.4

Browser version: not a browser bug

Browser OS version: not a browser bug

Original install method (e.g. download page, yum, from source, etc.): tarball from the website then extract

Describe the bug: It looks like there is a path variable that is empty and blocks the startup process of kibana. See the error log below.

Steps to reproduce:

1. Install kibana 7.2.0
2. Upgrade to 7.5.0
3. Run from command line: sudo -u elastic_kibana ./bin/kibana -c <config_file> --verbose

Expected behavior: kibana starts correctly

Screenshots (if relevant): N/A

Errors in browser console (if relevant): N/A

Provide logs and/or server output (if relevant):

  log   [16:31:16.794] [fatal][root] { ValidationError: child "path" fails because ["path" is not allowed to be empty]
    at Object.exports.process (/preveil/elastic_kibana/src/kibana-7.5.0-linux-x86_64/node_modules/joi/lib/errors.js:196:19)
    at internals.Object._validateWithOptions (/preveil/elastic_kibana/src/kibana-7.5.0-linux-x86_64/node_modules/joi/lib/types/any/index.js:675:31)
    at module.exports.internals.Any.root.validate (/preveil/elastic_kibana/src/kibana-7.5.0-linux-x86_64/node_modules/joi/lib/index.js:146:23)
    at Object.internals.implementation [as cookie] (/preveil/elastic_kibana/src/kibana-7.5.0-linux-x86_64/node_modules/hapi-auth-cookie/lib/index.js:94:25)
    at module.exports.internals.Auth._strategy (/preveil/elastic_kibana/src/kibana-7.5.0-linux-x86_64/node_modules/hapi/lib/auth.js:52:47)
    at createCookieSessionStorageFactory (/preveil/elastic_kibana/src/kibana-7.5.0-linux-x86_64/src/core/server/http/cookie_session_storage.js:86:15)
    at process._tickCallback (internal/process/next_tick.js:68:7)
  isJoi: true,
  name: 'ValidationError',
  details:
   [ { message: '"path" is not allowed to be empty',
       path: [Array],
       type: 'any.empty',
context: [Object] } ],
_object:
{ cookie: 'sid',
password: 'xxx',
validateFunc: [AsyncFunction: validateFunc],
isSecure: false,
path: '',
clearInvalid: true,
isHttpOnly: true,
isSameSite: false },
annotate: [Function] }
log   [16:31:16.799] [debug][server] stopping server
log   [16:31:16.800] [debug][legacy-service] stopping legacy service
log   [16:31:16.800] [debug][plugins-service] Stopping plugins service
log   [16:31:16.801] [debug][elasticsearch-service] Stopping elasticsearch service 

Any additional context:

[tehmoon]

From the stack trace, it looks like path: basePath, which is set to '' in my config, is the culprit.

Removing server.basePath made it work. I'll leave the ticket open in case you guys need to do anything.

[elasticmachine]

Pinging @elastic/kibana-operations (Team:Operations)

[elasticmachine]

Pinging @elastic/kibana-platform (Team:Platform)

[pgayvallet]

There has been a more explicit error message about the problem for a long time now

https://github.com/elastic/kibana/blob/dea26c64505c2d498000d93778d6051407a8b0d8/packages/core/http/core-http-server-internal/src/http_config.ts#L66-L70

Closing.