fix(gatsby): open lmdb instances in writeable locations in generated ssr/dsg function (#38631)

Author: pieh

packages/gatsby/src/utils/cache-lmdb.ts

@@ -13,7 +13,10 @@ const cacheDbFile =
       }`
     : `caches-lmdb`
 
-const dbPath = path.join(process.cwd(), `.cache/${cacheDbFile}`)
+const dbPath = path.join(
+  global.__GATSBY?.root || process.cwd(),
+  `.cache/${cacheDbFile}`
+)
 
 function getAlreadyOpenedStore(): RootDatabase | undefined {
   if (!globalThis.__GATSBY_OPEN_ROOT_LMDBS) {

packages/gatsby/src/utils/page-ssr-module/lambda.ts

@@ -23,7 +23,13 @@ function setupFsWrapper(): string {
   } catch (e) {
     // we are in a read-only filesystem, so we need to use a temp dir
 
-    const TEMP_CACHE_DIR = path.join(tmpdir(), `gatsby`, `.cache`)
+    const TEMP_DIR = path.join(tmpdir(), `gatsby`)
+    const TEMP_CACHE_DIR = path.join(TEMP_DIR, `.cache`)
+
+    global.__GATSBY = {
+      root: TEMP_DIR,
+      buildId: ``,
+    }
 
     // TODO: don't hardcode this
     const cacheDir = `/var/task/.cache`
@@ -148,8 +154,8 @@ async function getEngine(): Promise<GraphQLEngineType> {
         reject(error)
       })
     })
+    console.log(`Downloaded datastore from CDN`)
   }
-  console.log(`Downloaded datastore from CDN`)
 
   const graphqlEngine = new GraphQLEngine({
     dbPath,