How to access administration component in API Platforms distribution 2.4.2? - varnish

Question

I tried to set up API Platform on my local machine to explore it.
I tried to performed all the operations according to API Platform's "Getting Started" page. So I downloaded the latest offical distribution which happens to be v2.4.2 (https://github.com/api-platform/api-platform/releases/tag/v2.4.2) and I started it using Docker.
I cannot however access the administration backend at http://localhost:81 receiving "Unable to retrieve API documentation."
I searched for help at https://api-platform.com/docs/admin/getting-started/, but it describes steps that seems to be already done in the distribution
How can I enable the admin component or debug what went wrong?
Edit (2019-04-14)
$ docker container ls
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
40a5d5213cfe quay.io/api-platform/nginx "nginx -g 'daemon of…" 45 hours ago Up 6 minutes 0.0.0.0:8080->80/tcp apiplatformdemo_api_1
d53711c0ba0c quay.io/api-platform/php "docker-entrypoint p…" 45 hours ago Up 6 minutes 9000/tcp apiplatformdemo_php_1
2d4eb8d09e3e quay.io/api-platform/client "/bin/sh -c 'yarn st…" 45 hours ago Up 6 minutes 0.0.0.0:80->3000/tcp apiplatformdemo_client_1
abe3e3b41810 quay.io/api-platform/admin "/bin/sh -c 'yarn st…" 45 hours ago Up 6 minutes 0.0.0.0:81->3000/tcp apiplatformdemo_admin_1
4596a7f81cd8 postgres:10-alpine "docker-entrypoint.s…" 45 hours ago Up 6 minutes 0.0.0.0:5432->5432/tcp apiplatformdemo_db_1
c805fc2f11c9 dunglas/mercure "./mercure" 45 hours ago Up 6 minutes 443/tcp, 0.0.0.0:1337->80/tcp apiplatformdemo_mercure_1
Edit 2 (2019-04-14)
It is worth mentioning that although the API component at http://localhost:8080 works, the HTTPS variant at https://localhost:8443 does not. (Connection refused if I try to telnet it.)
Now it turned out it escaped my notice earlier that there is a message in the JS console saying there was a failed connection to https://localhost:8443. (It says about CORS, but I think the real reason is 8443 simply refuses connection). So although I entered the HTTP variant of Admin at http://localhost:81 it tried to access the API via HTTPS. What could be the reason HTTPS doesn't work?
Edit 3 (2019-04-15)
After looking into the logs of docker compose, I see it is relevant the Varnish container failed. h2-proxy depends on it and it is h2-proxy that governs the 8443 port.
cache-proxy_1 | Error:
cache-proxy_1 | Message from VCC-compiler:
cache-proxy_1 | Expected return action name.
cache-proxy_1 | ('/usr/local/etc/varnish/default.vcl' Line 67 Pos 13)
cache-proxy_1 | return (miss);
cache-proxy_1 | ------------####--
cache-proxy_1 |
cache-proxy_1 | Running VCC-compiler failed, exited with 2
cache-proxy_1 | VCL compilation failed
apiplatform242_cache-proxy_1 exited with code 2
h2-proxy_1 | 2019/04/15 08:09:17 [emerg] 1#1: host not found in upstream "cache-proxy" in /etc/nginx/conf.d/default.conf:58
h2-proxy_1 | nginx: [emerg] host not found in upstream "cache-proxy" in /etc/nginx/conf.d/default.conf:58
apiplatform242_h2-proxy_1 exited with code 1

Answer 1

I have solved this error by getting API Platform by cloning the current master and not download the tar.tgz release version (2.4.2)
git clone https://github.com/api-platform/api-platform.git
docker-compose build
docker-compose up -d
Works like a charm !