hashipi

commit b8921ed465349f5548cb4be8da274fbec13d3411
parent bf302a44fb488a5be571cc97a75b9f1d2b974698
Author: Andreas Gruhler <andreas.gruhler@adfinis.com>
Date:   Wed, 19 Jul 2023 23:39:06 +0200

doc: client-server architecture

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README.md
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1 file changed, 34 insertions(+), 0 deletions(-)
diff --git a/README.md b/README.md
@@ -4,6 +4,40 @@ A RaspberryPi test cluster for HashiCorp Vault and Nomad with Consul storage bac
 
 ![HashiPi](./img/HashiPi-small.jpg)
 
+## Client-Server Architecture
+The cluster can be built with 3 or 5 nodes.
+
+For 5 nodes, it is recommended to only have 3 server nodes for Nomad and Consul to keep the Raft traffic minimal.
+
+Example architecture with 5 RaspberyPi nodes:
+
+| Node | RAM | Nomad function | Consul function |
+|------|-----|----------------|-----------------|
+| 00   | 1GB | server         | client/server   |
+| 01   | 1GB | client         | client          |
+| 02   | 4GB | client/server  | client/server   |
+| 03   | 1GB | client         | client          |
+| 04   | 4GB | client/server  | client/server   |
+
+For best performance on low power devices, the [`raft_multiplier`](https://developer.hashicorp.com/consul/docs/install/performance) is set to the default value 5 (or higher):
+
+```
+performance {
+  raft_multiplier = 5
+}
+```
+
+The nomad clients have a higher [heartbeat timeout](https://developer.hashicorp.com/nomad/docs/configuration/server#client-heartbeats) set to make sure the low powered devices are not reported down too often:
+
+```
+# https://developer.hashicorp.com/nomad/docs/configuration/server#client-heartbeats
+# Increase heartbeat ttl under unreliable network conditions to prevent
+# client: error heartbeating. retrying: error="failed to update status: rpc
+# error: Not ready to serve consistent reads"
+heartbeat_grace = "30s"
+min_heartbeat_ttl = "30s"
+```
+
 ## ARM Builder 
 These Packer files use the [Packer builder for ARM](https://github.com/mkaczanowski/packer-builder-arm). Follow the instructions in the repo to setup the builder and use the provided [examples](https://github.com/mkaczanowski/packer-builder-arm/tree/master/boards) to modify to your liking.