Add Nexthop selection strategies and @strategy tag to remap.config.

[jrushford]

This PR adds NextHop selection strategies that may be used in place of the parent selection strategies in parent.config. The NextHop selection strategies are used in remap.config with a new @strategy tag. NextHop strategies are defined in a new config file, 'strategies.yaml'. When the remap.config is loaded, the NextHopStrategy factory loads the strategies.yaml and creates and configures instances of NextHopSelectionStrategies. When remap.config is parsed, a strategy is associated with a remap entry if there is a tag '@strategy=$name' in the config. If the strategy is configured for a remap, wrapper functions used for parent selection in HttpTransact will prefer the NextHopSelection strategies over the ParentSelection strategies when searchin for a NextHop or parent host. Sample strategy.yaml files are at proxy/http/remap/unit-tests.

[a-canary]

This is a big PR. I'll try to read through this over the next week.

[randall]

I'm happy with the general format here. (strategies, groups, hosts). Personally, I find the #include business weird. Maybe what Alan suggested with include: [filename.yaml, file2.yaml] is better. I don't have a strong enough option here to argue either way.

[jrushford]

@randall the #include is used to concatenate multiple file streams into a single stream as a single YAML document that then may be parsed. @AMC idea of using 'include: [ file1.yaml, file2.yaml] complicates this IMHO. I'd have to parse a partial YAML file, look for a YAML 'include:' name space then re-read all the files so that I can then parse 'strategies'. I think this makes it too complicated and I think the '#include file' is simpler and more flexible. I do like @AMC's idea of reading a directory and concatenating YAML files in 'ls' order and I'll probably add that. But, using a YAML list to include other files just seems to complicated to me so, I'm leaving the '#include' for now.

[a-canary]

Lots of comments and questions. Only blocking concerns are:

• REMAP_OPTFLG_STRATEGY 0x800000000u is too big.
• NextHopSelectionStrategy::markNextHopDown isn't called from anywhere.

[jrushford]

Lots of comments and questions. Only blocking concerns are:

• REMAP_OPTFLG_STRATEGY 0x800000000u is too big.
• NextHopSelectionStrategy::markNextHopDown isn't called from anywhere.

@a-canary this is fixed.

[jrushford]

rebased to pick up fix for FreeBSD CI build

[a-canary]

+1

[gtenev]

I am still looking into this PR

[vmamidi]

@gtenev is looking into this PR.

[a-canary]

@gtenev @vmamidi This code isn't perfect. But it's a step in the right direction. I expect this to evolve and mature greatly over the next few releases. We'll start testing this for production in Q1.

[vmamidi]

+1. I agree I’ve already seen the code. I am now waiting for Gancho’s feedback.

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On Nov 12, 2019, at 7:48 AM, a-a-ron ***@***.***> wrote:  @gtenev @vmamidi This code isn't perfect. But it's a step in the right direction. I expect this to evolve and mature greatly over the next few releases. We'll start testing this for production in Q1. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub, or unsubscribe.

[jrushford]

rebased to pick up yaml 0.6.3 update.

[calavera]

this looks very useful. I really like the failover strategies part 👍

[jrushford]

@calavera still working on some review comments. It'll go in soon.

[zwoop]

This is breaking big time on the CI, segfaulting the tests.