Remove Redis/Cachex dependency, use pure ETS for caching

- Replace Cachex with native ETS (Erlang Term Storage) in Cache module
- Remove Redis-based caching logic from application.ex
- Always initialize ETS tables for device_cache, query_cache, symbol_cache
- Update StatusLive to use Aprsme.Cache instead of Cachex directly
- Fix crash on startup when REDIS_URL was set but Redis not used

This fixes the no_cache error that was causing pods to crash.

lib/aprsme/application.ex

@@ -235,24 +235,18 @@ defmodule Aprsme.Application do
   # end
 
   defp redis_children do
-    if System.get_env("REDIS_URL") do
-      require Logger
+    require Logger
 
-      Logger.info("Starting Redis-based caching and rate limiting")
+    Logger.info("Starting ETS-based caching and rate limiting")
 
-      []
-    else
-      require Logger
+    # Create ETS tables for caching
+    :ets.new(:query_cache, [:set, :public, :named_table, read_concurrency: true])
+    :ets.new(:device_cache, [:set, :public, :named_table, read_concurrency: true])
+    :ets.new(:symbol_cache, [:set, :public, :named_table, read_concurrency: true])
 
-      Logger.info("Starting ETS-based caching and rate limiting (no Redis URL)")
-
-      [
-        # Fallback to ETS-based implementations
-        Aprsme.RateLimiter,
-        %{id: :query_cache, start: {Cachex, :start_link, [:query_cache, [limit: 10_000]]}},
-        %{id: :device_cache, start: {Cachex, :start_link, [:device_cache, [limit: 5_000]]}},
-        %{id: :symbol_cache, start: {Cachex, :start_link, [:symbol_cache, [limit: 1_000]]}}
-      ]
-    end
+    [
+      # ETS-based rate limiter
+      Aprsme.RateLimiter
+    ]
   end
 end

lib/aprsme/cache.ex

@@ -1,59 +1,85 @@
 defmodule Aprsme.Cache do
   @moduledoc """
-  Cache abstraction layer that works with both Cachex and RedisCache.
-  Provides a unified API regardless of the underlying implementation.
+  Cache abstraction layer using ETS (Erlang Term Storage).
+  Provides a unified API for in-memory caching.
   """
 
   @doc """
   Get a value from cache
   """
   def get(cache_name, key) do
-    Cachex.get(cache_name, key)
+    case :ets.lookup(cache_name, key) do
+      [{^key, value}] -> {:ok, value}
+      [] -> {:ok, nil}
+    end
+  rescue
+    ArgumentError -> {:error, :no_cache}
   end
 
   @doc """
-  Put a value in cache with optional TTL
+  Put a value in cache with optional TTL (TTL not implemented for ETS)
   """
-  def put(cache_name, key, value, opts \\ []) do
-    Cachex.put(cache_name, key, value, opts)
+  def put(cache_name, key, value, _opts \\ []) do
+    try do
+      :ets.insert(cache_name, {key, value})
+      {:ok, true}
+    rescue
+      ArgumentError -> {:error, :no_cache}
+    end
   end
 
   @doc """
   Delete a key from cache
   """
   def del(cache_name, key) do
-    Cachex.del(cache_name, key)
+    try do
+      :ets.delete(cache_name, key)
+      {:ok, true}
+    rescue
+      ArgumentError -> {:error, :no_cache}
+    end
   end
 
   @doc """
   Clear all keys from cache
   """
   def clear(cache_name) do
-    Cachex.clear(cache_name)
+    try do
+      :ets.delete_all_objects(cache_name)
+      {:ok, true}
+    rescue
+      ArgumentError -> {:error, :no_cache}
+    end
   end
 
   @doc """
-  Get cache statistics
+  Get cache statistics (simplified for ETS)
   """
   def stats(cache_name) do
-    Cachex.stats(cache_name)
+    try do
+      info = :ets.info(cache_name)
+      {:ok, %{size: Keyword.get(info, :size, 0)}}
+    rescue
+      ArgumentError -> {:error, :no_cache}
+    end
   end
 
   @doc """
   Check if key exists
   """
   def exists?(cache_name, key) do
-    case Cachex.exists?(cache_name, key) do
-      {:ok, exists?} -> exists?
-      {:error, _reason} -> false
+    try do
+      :ets.member(cache_name, key)
+    rescue
+      ArgumentError -> false
     end
   end
 
   @doc """
-  Get TTL for a key
+  Get TTL for a key (not supported in ETS, always returns nil)
   """
-  def ttl(cache_name, key) do
-    Cachex.ttl(cache_name, key)
+  def ttl(_cache_name, _key) do
+    {:ok, nil}
   end
 
   # Helper functions - no longer needed as we only use Cachex

lib/aprsme_web/live/status_live/index.ex

@@ -395,14 +395,14 @@ defmodule AprsmeWeb.StatusLive.Index do
 
   defp get_cached_aprs_status do
     # Try to get cached status for instant load
-    case Cachex.get(:query_cache, "aprs_status") do
+    case Aprsme.Cache.get(:query_cache, "aprs_status") do
       {:ok, status} when not is_nil(status) ->
         status
 
       _ ->
         # Fallback to direct query if cache miss
         status = get_aprs_status()
-        Cachex.put(:query_cache, "aprs_status", status, ttl: to_timeout(second: 5))
+        Aprsme.Cache.put(:query_cache, "aprs_status", status)
         status
     end
   end