All CLA requirements met.

Do we need an explicit file for this ?

Can you infer the same through r/w mode of one/more paths mapped into container ?

For example, which path should be mounted as rw for non-read-onlly mode?
And if this path is instead mounted as read-only, you know this run has to be in read-only mode.

I suppose we could put the file in the telemetry container instead of on the host, would this be better?. I am not sure about mounting a volume ro vs rw, I don't know which volume we would use for this or why.

Curious, what is the difference between read-only & read-write mode for telemetry docker?

There was a request to have a read-only mode for telemetry since some do not want to use telemetry for configuration. The read-only mode will disable the Set() rpc so there is only Get, Subscribe and Capabilities rpc's available.

Just one more question:
Once an image is built as read-only or read-write mode, can it be changed during runtime?

If not, why can't we use a compile time flag to build it as read-only / read-write?

Using the current method of looking for a file, you could disable read-only mode by removing the file. As for the compile time flag, that is an option as well which I considered. Would it be preferable this way?

When looking at build flags, I thought I would need to make duplicate source files like server.go and server_ro.go for example. However looking at more examples, I could rather have a file like constants_rw.go and constants_ro.go and define a single "const TELEMETRY_RO" in each file which would be set by the build flag. So this is a good option as well. If this is preferred, I can redo this PR to use this method.

Please check with relevant folks, who were requesting for read-only mode, if this suits.

"An image is built for RO/RW mode as immutable"

I checked. The mode is burnt into the image. So we can use a build time flag to decide

@renukamanavalan Please see the latest commit. I switched to using a go build flag instead of the file method. Now the readonly mode is set at build time in a constant inside the telemetry binary, so is immutable.

Can you please help understand how does this BLDFLAG '-tag helps include the correct constant file ?

It is a build constraint: https://golang.org/pkg/go/build/#hdr-Build_Constraints
Using the -tags allows you to specify them at build time and determine which files will be included.

Can we make read-only as default ?

Sure I will make this change.

Okay, I have changed the default to read-only.

suggest to the read-only default.

read only default

This is already the case. renukamanavalan already requested this in a previous comment and I made the changes to have it readonly by default.