stellar#141: review feedback, tx sub changes

docs/run-platform-server/configuring.mdx

@@ -46,7 +46,7 @@ You need to allocate **at least** one instance to perform ongoing ingestion to c
 
 ### API Role Instance
 
-You can run none or multiple instances to serve read only API requests.
+You can run none or multiple instances to serve read only API requests. Notice there is no need to define network settings here, as Horizon only reads from database.
 
 **TODO - create TX_SUB_ENABLED env variable, default=true. Should return 405 on POSTs to /tx if FALSE. If true, horizon should check at startup that ingestion is happening on it's db or exit startup with error. If TX_SUB_ENABLED=FALSE and INGEST=FALSE, should also allow skipping need to define `NETWORK` or `STELLAR_CORE_URL` since there is no need to be aware of core.**
 
@@ -58,12 +58,14 @@ You can run none or multiple instances to serve read only API requests.
 
 ### Transaction Submission Role Instance
 
-You can run none or multiple instances to serve transaction submission requests. If you run an instance with transaction submission enabled, your deployment is required to perform the ingestion role on the same database referenced here. Horizon transaction submission depends on ingestion to confirm tx submission status.
+You can run none or multiple instances to serve transaction submission requests. If you run an instance with transaction submission enabled, your deployment is required to perform the ingestion role on the same database referenced here. Horizon transaction submission depends on **live** ingestion to confirm tx submission status.
 
 If ingestion is planned to be done on a separate instance, add `INGEST=false` on this instance, otherwise don't include the parameter, Horizon will default to `INGEST=true` if absent.
 
 If not using the `NETWORK` variable, then must provide the `STELLAR_CORE_URL` variable.
 
+Refer to [Channel Accounts](../encyclopedia/channel-accounts.mdx) for some recommendations on client transaction submission optimizations.
+
 **TODO - Confirm Horizon can use captive core to send tx sub requests and skip stellar-core-url?. **
 
 | environment variable | example                             |
@@ -76,6 +78,11 @@ If not using the `NETWORK` variable, then must provide the `STELLAR_CORE_URL` va
 
 - If you have configured your deployment to perform the ingestion role, then it is **strongly** recommended to review [Ingestion](./ingestion.mdx) first and [Filtering](./ingestion-filtering) second and factor that into configuration parameters to achieve best performance related to your application requirements before proceeding further.
 
+- `TX_SUB_ENABLED`, optional, enabled as TRUE by default.
+
+  - When enabled, requires **live** ingestion process to be running on the same database because Horizon depends on new ledgers from network to confirm a transaction submission status, Horizon will report startup error if it detects no **live** ingestion. Requires `NETWORK` or `STELLAR_CORE_URL` be defined for access to network.
+  - When disabled with FALSE, Horizon will return 405 on POSTs to /tx.
+
 - `NETWORK`, optional, can be one of Stellar's public networks, 'pubnet', or 'devnet'. Triggers horizon to automatically set configurations for remaining horizon settings and generate the correct core toml/cfg settings. If you only need Horizon to connect to one of those public Stellar networks, this will take care of all related configuration.
 
 **TODO - create the new `NETWORK` env variable and the functionality it performs to configure all aspects of network connection, including toml, passphrase, archive urls, etc for networks 'pubnet' and 'testnet'. Refer to quickstart for example of same consolidated config parameter for setting network. **