Can't start osqueryd test instances via docker-compose on Linux

[nyanshak]

What version of fleet are you using (fleet version --full)?

d453ca3 (master)

What operating system are you using?

Linux

uname -a
Linux <hostname> 5.3.7-arch1-2-ARCH #1 SMP PREEMPT @1572002934 x86_64 GNU/Linux

What did you do?

Following tools/osquery/README.md:

export KOLIDE_OSQUERY_VERSION="latest"
export ENROLL_SECRET="<secret>"
docker-compose up

What did you expect to see?

4 test hosts connecting to fleet locally

What did you see instead?

centos7-osquery_1   | W1101 02:15:39.805672     8 tls_enroll.cpp:75] Failed enrollment request to https://host.docker.internal:8080/api/v1/osquery/enroll (Request error: Host not found (authoritative)) retrying...

It looks like previously, this file used extra_hosts block in compose file to add an extra host called dockerhost set to the env var $LOCALHOST, then used dockerhost in the tls_hostname in the flag file.

In #2019, this was changed to use host.docker.internal instead, with tls_hostname set to host.docker.internal, to enable starting osquery instances with less configuration.

However, Docker on Linux does not add the host.docker.internal DNS name, so this prevents starting the osqueryd test containers from connecting to fleet on Linux machines.