Update ROADMAP and constraints

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

README.md

@@ -150,9 +150,13 @@ See [here for manual / developer instructions](docs/DEV.md)
 
 ## Getting help
 
-### Docs
+### faasd handbook
 
-The [OpenFaaS docs](https://docs.openfaas.com/) provide a wealth of information and are kept up to date with new features.
+Get early access to the faasd handbook through an [OpenFaaS GitHub Sponsorship](https://github.com/sponsors/openfaas/)
+
+### Reference docs for Kubernetes
+
+The [OpenFaaS docs](https://docs.openfaas.com/) provide a wealth of information for OpenFaaS on Kubernetes, and are likely to be useful for you, even using faasd.
 
 ### Function and template store
 
@@ -181,56 +185,7 @@ If you are learning faasd, or want to share your use-case, you can join the Open
 * [Become an OpenFaaS GitHub Sponsor](https://github.com/sponsors/openfaas/)
 * [Join Slack](https://slack.openfaas.io/)
 
-
+### Backlog, features and known issues
-## Roadmap
-
-### Supported operations
-
-* `faas login`
-* `faas up`
-* `faas list`
-* `faas describe`
-* `faas deploy --update=true --replace=false`
-* `faas invoke --async`
-* `faas invoke`
-* `faas rm`
-* `faas store list/deploy/inspect`
-* `faas version`
-* `faas namespace`
-* `faas secret`
-* `faas logs`
-
-Scale from and to zero is also supported. On a Dell XPS with a small, pre-pulled image unpausing an existing task took 0.19s and starting a task for a killed function took 0.39s. There may be further optimizations to be gained.
-
-Other operations are pending development in the provider such as:
-
-* `faas auth` - supported for Basic Authentication, but SSO, OAuth2 & OIDC may require a patch
-
-### Known-issues
-
-#### Non 200 HTTP status code upon first use
-
-This issue appears to happen sporadically and only for some users.
-
-If you get a non 200 HTTP code from the gateway, or caddy after installing faasd, check the logs of faasd:
-
-```bash
-sudo journalctl -t faasd
-```
-
-If you see the following error:
-
-```
-unable to dial to 10.62.0.5:8080, error: dial tcp 10.62.0.5:8080: connect: no route to host
-```
-
-Restart the faasd service with:
-
-```bash
-sudo systemctl restart faasd
-```
-
-### Backlog and features
 
 For completed features, WIP and upcoming roadmap see:
 

docs/ROADMAP.md

@@ -1,5 +1,76 @@
 # faasd backlog and features
 
+## Supported operations
+
+* `faas login`
+* `faas up`
+* `faas list`
+* `faas describe`
+* `faas deploy --update=true --replace=false`
+* `faas invoke --async`
+* `faas invoke`
+* `faas rm`
+* `faas store list/deploy/inspect`
+* `faas version`
+* `faas namespace`
+* `faas secret`
+* `faas logs`
+* `faas auth` - supported for Basic Authentication and OpenFaaS PRO with OIDC and Single-sign On.
+
+Scale from and to zero is also supported. On a Dell XPS with a small, pre-pulled image unpausing an existing task took 0.19s and starting a task for a killed function took 0.39s. There may be further optimizations to be gained.
+
+## Constraints vs OpenFaaS on Kubernetes
+
+faasd suits certain use-cases as mentioned in the README file, for those who want a solution which can scale out horizontally with minimum effort, Kubernetes or K3s is a valid option.
+
+### One replica per function
+
+Functions only support one replica, so cannot scale horizontally, but can scale vertically.
+
+Workaround: deploy one uniquely named function per replica.
+
+### Scale from zero may give a non-200
+
+When scaling from zero there is no health check implemented, so the request may arrive before your HTTP server is ready to serve a request, and therefore give a non-200 code.
+
+Workaround: Do not scale to zero, or have your client retry HTTP calls.
+
+### No clustering is available
+
+No clustering is available in faasd, however you can still apply fault-tolerance and high availability techniques.
+
+Workaround: deploy multiple faasd instances and use a hardware or software load-balancer. Take regular VM/host snapshots or backups.
+
+### No rolling updates
+
+When running `faas-cli deploy`, your old function is removed before the new one is started. This may cause a small amount of downtime, depending on the timeouts and grace periods you set.
+
+Workaround: deploy uniquely named functions per version, and switch an Ingress or Reverse Proxy record to point at a new version once it is ready.
+
+## Known issues
+
+### Non 200 HTTP status from the gateway upon first use
+
+This issue appears to happen sporadically and only for some users.
+
+If you get a non 200 HTTP code from the gateway, or caddy after installing faasd, check the logs of faasd:
+
+```bash
+sudo journalctl -t faasd
+```
+
+If you see the following error:
+
+```
+unable to dial to 10.62.0.5:8080, error: dial tcp 10.62.0.5:8080: connect: no route to host
+```
+
+Restart the faasd service with:
+
+```bash
+sudo systemctl restart faasd
+```
+
 ## Backlog
 
 Should have:
@@ -42,3 +113,4 @@ Nice to Have:
 * [x] Terraform for DigitalOcean
 * [x] [Store and retrieve annotations in function spec](https://github.com/openfaas/faasd/pull/86) - in progress
 * [x] An installer for faasd and dependencies - runc, containerd
+