Fix a startup race: the app connects to Postgres immediately and fails when the database is not yet ready. Add retry/backoff logic so the app waits for Postgres to be ready.
Our app keeps failing on startup with "connection refused" to Postgres. It seems like the app starts before the database is ready. How do we fix that?
The user has a Docker/container startup ordering issue where their app tries to connect to Postgres before it's ready. Let me look at their project files to understand the setup.
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No files found
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{"command":"ls /app 2>/dev/null || ls /opt 2>/dev/null || ls /srv 2>/dev/null || ls /home 2>/dev/null; find / -maxdepth 3 -name \"supervisord.conf\" -o -name \"supervisor.conf\" 2>/dev/null","description":"Find app directory and supervisor config"}dec-bench redpanda /etc/supervisord.conf /etc/supervisor/supervisord.conf /scenario/supervisord.conf
{"file_path":"/etc/supervisord.conf"}{"command":"ls /scenario/","description":"List scenario directory"}1 [supervisord] 2 nodaemon=false 3 logfile=/tmp/supervisord.log 4 pidfile=/tmp/supervisord.pid 5 6 [program:postgres] 7 command=/usr/lib/postgresql/16/bin/postgres -D /var/lib/postgresql/data 8 user=postgres 9 autostart=true 10 autorestart=false 11 priority=10 12 stdout_logfile=...
assertions init prompts scenario.json supervisord.conf
{"file_path":"/scenario/supervisord.conf"}{"command":"ls /scenario/init/","description":"List init directory"}1 [supervisord] 2 nodaemon=false 3 logfile=/tmp/supervisord.log 4 pidfile=/tmp/supervisord.pid 5 6 [program:postgres] 7 command=/usr/lib/postgresql/16/bin/postgres -D /var/lib/postgresql/data 8 user=postgres 9 autostart=true 10 autorestart=false 11 priority=10 12 stdout_logfile=...
postgres-setup.sql setup-broken-startup.sh
{"file_path":"/scenario/init/setup-broken-startup.sh"}{"file_path":"/scenario/init/postgres-setup.sql"}{"command":"ls /opt/","description":"List opt directory"}1 CREATE SCHEMA IF NOT EXISTS app; 2 3 CREATE TABLE app.health ( 4 id SERIAL PRIMARY KEY, 5 checked_at TIMESTAMPTZ DEFAULT now() 6 ); 7
1 #!/bin/bash
2 mkdir -p /workspace
3
4 cat > /workspace/start_app.py << 'PYEOF'
5 import psycopg2
6 import os
7 # Broken: no retry - fails if Postgres not ready
8 conn = psycopg2.connect(os.environ.get("POSTGRES_URL", "postgresql://postgres@localhost:5432/postgres"))
9 conn.clo...dec-bench redpanda
Now I see the issue. The app at `/workspace/start_app.py` connects to Postgres with no retry logic. Let me fix it.
{"file_path":"/workspace/start_app.py"}1 import psycopg2
2 import os
3 # Broken: no retry - fails if Postgres not ready
4 conn = psycopg2.connect(os.environ.get("POSTGRES_URL", "postgresql://postgres@localhost:5432/postgres"))
5 conn.close()
6 print("Connected")
7 {"file_path":"/workspace/start_app.py","content":"import psycopg2\nimport os\nimport time\n\nmax_retries = 30\nretry_delay = 1\n\nfor attempt in range(1, max_retries + 1):\n try:\n conn = psycopg2.connect(os.environ.get(\"POSTGRES_URL\", \"postgresql://postgres@localhos...The file /workspace/start_app.py has been updated successfully.
Now let me verify it works by starting Postgres and running the script.
{"command":"supervisord -c /etc/supervisord.conf && sleep 2 && python3 /workspace/start_app.py","description":"Start Postgres and test the app","timeout":30000}Connected
The fix is working. Here's what I changed in `/workspace/start_app.py`: **Problem:** The app tried to connect to Postgres once with no retry logic. If Postgres wasn't fully ready to accept connections yet, the app would immediately crash with "connection refused." **Fix:** Adde...
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"content": "1\tCREATE SCHEMA IF NOT EXISTS app;\n2\t\n3\tCREATE TABLE app.health (\n4\t id SERIAL PRIMARY KEY,\n5\t checked_at TIMESTAMPTZ DEFAULT now()\n6\t);\n7\t"
},
{
"id": "evt-29",
"kind": "tool_result",
"role": "tool",
"timestamp": "2026-04-08T15:12:10.483Z",
"toolUseId": "toolu_01JctAVf77CDwVHUx3RaBvNn",
"toolName": "Read",
"isError": false,
"content": "1\t#!/bin/bash\n2\tmkdir -p /workspace\n3\t\n4\tcat > /workspace/start_app.py << 'PYEOF'\n5\timport psycopg2\n6\timport os\n7\t# Broken: no retry - fails if Postgres not ready\n8\tconn = psycopg2.connect(os.environ.get(\"POSTGRES_URL\", \"postgresql://postgres@localhost:5432/postgres\"))\n9\tconn.close()\n10\tprint(\"Connected\")\n11\tPYEOF\n12\t\n13\techo \"Broken startup script created.\""
},
{
"id": "evt-30",
"kind": "tool_result",
"role": "tool",
"timestamp": "2026-04-08T15:12:10.490Z",
"toolUseId": "toolu_011AQ1Wc2guDzNfKc54zExKb",
"toolName": "Bash",
"isError": false,
"content": "dec-bench\nredpanda"
},
{
"id": "evt-31",
"kind": "assistant_text",
"role": "assistant",
"model": "claude-opus-4-6",
"timestamp": "2026-04-08T15:12:13.304Z",
"content": "Now I see the issue. The app at `/workspace/start_app.py` connects to Postgres with no retry logic. Let me fix it."
},
{
"id": "evt-32",
"kind": "tool_use",
"role": "assistant",
"model": "claude-opus-4-6",
"timestamp": "2026-04-08T15:12:13.459Z",
"name": "Read",
"toolUseId": "toolu_01KYdxmtBprng23H4UYWp8v8",
"input": {
"file_path": "/workspace/start_app.py"
}
},
{
"id": "evt-33",
"kind": "tool_result",
"role": "tool",
"timestamp": "2026-04-08T15:12:13.483Z",
"toolUseId": "toolu_01KYdxmtBprng23H4UYWp8v8",
"toolName": "Read",
"isError": false,
"content": "1\timport psycopg2\n2\timport os\n3\t# Broken: no retry - fails if Postgres not ready\n4\tconn = psycopg2.connect(os.environ.get(\"POSTGRES_URL\", \"postgresql://postgres@localhost:5432/postgres\"))\n5\tconn.close()\n6\tprint(\"Connected\")\n7\t"
},
{
"id": "evt-34",
"kind": "tool_use",
"role": "assistant",
"model": "claude-opus-4-6",
"timestamp": "2026-04-08T15:12:18.410Z",
"name": "Write",
"toolUseId": "toolu_015P9iRZM1BSH3HU7C7XFffD",
"input": {
"file_path": "/workspace/start_app.py",
"content": "import psycopg2\nimport os\nimport time\n\nmax_retries = 30\nretry_delay = 1\n\nfor attempt in range(1, max_retries + 1):\n try:\n conn = psycopg2.connect(os.environ.get(\"POSTGRES_URL\", \"postgresql://postgres@localhost:5432/postgres\"))\n conn.close()\n print(\"Connected\")\n break\n except psycopg2.OperationalError:\n if attempt == max_retries:\n raise\n print(f\"Postgres not ready (attempt {attempt}/{max_retries}), retrying in {retry_delay}s...\")\n time.sleep(retry_delay)\n"
}
},
{
"id": "evt-35",
"kind": "tool_result",
"role": "tool",
"timestamp": "2026-04-08T15:12:18.638Z",
"toolUseId": "toolu_015P9iRZM1BSH3HU7C7XFffD",
"toolName": "Write",
"isError": false,
"content": "The file /workspace/start_app.py has been updated successfully."
},
{
"id": "evt-36",
"kind": "assistant_text",
"role": "assistant",
"model": "claude-opus-4-6",
"timestamp": "2026-04-08T15:12:21.295Z",
"content": "Now let me verify it works by starting Postgres and running the script."
},
{
"id": "evt-37",
"kind": "tool_use",
"role": "assistant",
"model": "claude-opus-4-6",
"timestamp": "2026-04-08T15:12:21.859Z",
"name": "Bash",
"toolUseId": "toolu_01T2f2nwNWGLzryrAY1CDgjm",
"input": {
"command": "supervisord -c /etc/supervisord.conf && sleep 2 && python3 /workspace/start_app.py",
"description": "Start Postgres and test the app",
"timeout": 30000
}
},
{
"id": "evt-38",
"kind": "tool_result",
"role": "tool",
"timestamp": "2026-04-08T15:12:24.047Z",
"toolUseId": "toolu_01T2f2nwNWGLzryrAY1CDgjm",
"toolName": "Bash",
"isError": false,
"content": "Connected"
},
{
"id": "evt-39",
"kind": "assistant_text",
"role": "assistant",
"model": "claude-opus-4-6",
"timestamp": "2026-04-08T15:12:29.409Z",
"content": "The fix is working. Here's what I changed in `/workspace/start_app.py`:\n\n**Problem:** The app tried to connect to Postgres once with no retry logic. If Postgres wasn't fully ready to accept connections yet, the app would immediately crash with \"connection refused.\"\n\n**Fix:** Added a retry loop that:\n- Attempts to connect up to **30 times** with a **1-second delay** between attempts\n- Prints a status message on each failed attempt\n- Only raises the error if all retries are exhausted\n- Succeeds immediately once Postgres is ready\n\nThis is a standard \"wait-for-dependency\" pattern for services that start concurrently with their databases."
}
]
}Debugging Output
6 files · 84KBHarness
base-rt
Agent
claude-code
Model
claude-opus-4-6
Version
v0.1.0
Persona
baseline
Plan Mode
no-plan
Prompt
Current
Our app keeps failing on startup with "connection refused" to Postgres. It seems like the app starts before the database is ready. How do we fix that?
ID
foo-bar-postgres-readiness-race
Domain
foo-bar
Tier
tier-1
Harness
base-rt
Postgres and a Python app. The app's startup script connects immediately and fails if Postgres is not ready.
Add retry logic with backoff to the startup script so it waits for Postgres before connecting.