b19583e7d3
This is an initial implementation of the mgmt language. It is a declarative (immutable) functional, reactive, domain specific programming language. It is intended to be a language that is: * safe * powerful * easy to reason about With these properties, we hope this language, and the mgmt engine will allow you to model the real-time systems that you'd like to automate. This also includes a number of other associated changes. Sorry for the large size of this patch.
92 lines
4.4 KiB
Markdown
92 lines
4.4 KiB
Markdown
# Frequently asked questions
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(Send your questions as a patch to this FAQ! I'll review it, merge it, and
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respond by commit with the answer.)
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### Why did you start this project?
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I wanted a next generation config management solution that didn't have all of
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the design flaws or limitations that the current generation of tools do, and no
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tool existed!
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### Why did you use etcd? What about consul?
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Etcd and consul are both written in golang, which made them the top two
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contenders for my prototype. Ultimately a choice had to be made, and etcd was
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chosen, but it was also somewhat arbitrary. If there is available interest,
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good reasoning, *and* patches, then we would consider either switching or
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supporting both, but this is not a high priority at this time.
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### Can I use an existing etcd cluster instead of the automatic embedded servers?
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Yes, it's possible to use an existing etcd cluster instead of the automatic,
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elastic embedded etcd servers. To do so, simply point to the cluster with the
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`--seeds` variable, the same way you would if you were seeding a new member to
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an existing mgmt cluster.
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The downside to this approach is that you won't benefit from the automatic
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elastic nature of the embedded etcd servers, and that you're responsible if you
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accidentally break your etcd cluster, or if you use an unsupported version.
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### What does the error message about an inconsistent dataDir mean?
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If you get an error message similar to:
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```
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Etcd: Connect: CtxError...
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Etcd: CtxError: Reason: CtxDelayErr(5s): No endpoints available yet!
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Etcd: Connect: Endpoints: []
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Etcd: The dataDir (/var/lib/mgmt/etcd) might be inconsistent or corrupt.
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```
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This happens when there are a series of fatal connect errors in a row. This can
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happen when you start `mgmt` using a dataDir that doesn't correspond to the
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current cluster view. As a result, the embedded etcd server never finishes
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starting up, and as a result, a default endpoint never gets added. The solution
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is to either reconcile the mistake, and if there is no important data saved, you
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can remove the etcd dataDir. This is typically `/var/lib/mgmt/etcd/member/`.
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### Why do resources have both a `Compare` method and an `IFF` (on the UID) method?
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The `Compare()` methods are for determining if two resources are effectively the
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same, which is used to make graph change delta's efficient. This is when we want
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to change from the current running graph to a new graph, but preserve the common
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vertices. Since we want to make this process efficient, we only update the parts
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that are different, and leave everything else alone. This `Compare()` method can
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tell us if two resources are the same.
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The `IFF()` method is part of the whole UID system, which is for discerning if a
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resource meets the requirements another expects for an automatic edge. This is
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because the automatic edge system assumes a unified UID pattern to test for
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equality. In the future it might be helpful or sane to merge the two similar
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comparison functions although for now they are separate because they are
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actually answer different questions.
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### Does this support Windows? OSX? GNU Hurd?
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Mgmt probably works best on Linux, because that's what most developers use for
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serious automation workloads. Support for non-Linux operating systems isn't a
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high priority of mine, but we're happy to accept patches for missing features
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or resources that you think would make sense on your favourite platform.
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### Did you know that there is a band named `MGMT`?
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I didn't realize this when naming the project, and it is accidental. After much
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anguishing, I chose the name because it was short and I thought it was
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appropriately descriptive. If you need a less ambiguous search term or phrase,
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you can try using `mgmtconfig` or `mgmt config`.
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It also doesn't stand for
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[Methyl Guanine Methyl Transferase](https://en.wikipedia.org/wiki/O-6-methylguanine-DNA_methyltransferase)
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which definitely existed before the band did.
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### You didn't answer my question, or I have a question!
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It's best to ask on [IRC](https://webchat.freenode.net/?channels=#mgmtconfig)
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to see if someone can help you. Once we get a big enough community going, we'll
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add a mailing list. If you don't get any response from the above, you can
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contact me through my [technical blog](https://purpleidea.com/contact/)
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and I'll do my best to help. If you have a good question, please add it as a
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patch to this documentation. I'll merge your question, and add a patch with the
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answer!
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