Add CYGNUS_CONF_URL to fetch a custom agent config w/o rebuilding docker image

[taliaga]

Hi there!

I'm new to cygnus, but I'm proposing this little change to make it easier to try different agent configurations without the need to rebuild the image. This way, I can put the agent config in, say, a github gist and try different things faster.

Note that I'm including some COPY in the Dockerfile because when building locally an image, a change in one of those script is actually being ignored. There's a non-trivial flow of variables definition and copies in the huge RUN command above, which ends up using the script in the configured cygnus repo. I couldn't see the need for such indirection... maybe from the time the Dockerfile was not inside the repo?

Anyway, let me know wdyt :)

[frbattid]

I'll review this ASAP, thanks!

[taliaga]

@frbattid Another benefit I forgot to mention regarding this, consequence of the fact that rebuilding the image is no longer necessary, is that it makes much easier testing cygnus in a distributed cluster environment (a docker swarm cluster is my use case).

[taliaga]

Hi @AlvaroVega!, any comments on this? I'd like to stop using my custom cygnus images if possible.

[AlvaroVega]

HI, was this PR tested? Does this PR ensure backward compatibility?

[taliaga]

Thanks Alvaro for such a fast reply.
So, first of all, as a developer I understand your concerns.
Also, note that the changes I'm doing are within the docker folder, not source code already being tested.

That being said, my question is... what kind of testing for this would you like to have?

• The basic one: Yes, I've tested it locally and it works both ways of the "if" (i.e, with and without config file url). It's expected to be backwards compatible because I'm just adding functionality only when a new variable is present ($CYGNUS_CONF_URL).
• The fact that it's a valid dockerfile: we could try to get the hub.docker.com build the image with the source of this branch. But that will not assure you anything about backwards compatibility.
• Something more complex you may have in mind?

[taliaga]

Ping @AlvaroVega

[taliaga]

@AlvaroVega @

[AlvaroVega]

Regarding with this PR currently you can use CYGNUS_SKIP_CONF_GENERATION env var and others to provide your custom agent configuration.
Download that custom agent configuration is not included.

[AlvaroVega]

Using docker, currently you can provide your own cygnus agent conf in a file in a volumen.

[fgalan]

Using docker, currently you can provide your own cygnus agent conf in a file in a volumen.

@taliaga is enough with this possiblity that @AlvaroVega explains? Or do you still that downloading a conf file (using wget) is still needed? In the second case, could you elaborate on the user case behind, please?

Thanks!